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UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, DC 20549

FORM N-CSRS

CERTIFIED SHAREHOLDER REPORT OF REGISTERED

MANAGEMENT INVESTMENT COMPANIES

Investment Company Act file number 811-4815

Ultra Series Fund
(Exact name of registrant as specified in charter)

550 Science Drive, Madison, WI 53711
(Address of principal executive offices)(Zip code)

Kevin S. Thompson
Chief Legal Officer
550 Science Drive
Madison, WI 53711
(Name and address of agent for service)

Registrant’s telephone number, including area code: 608-274-0300

Date of fiscal year end: December 31

Date of reporting period: June 30, 2017

Form N-CSRS is to be used by management investment companies to file reports with the Commission not later than 10 days after the transmission to stockholders of any report that is required to be transmitted to stockholders under Rule 30e-1 under the Investment Company Act of 1940 (17 CFR 270.30e-1). The Commission may use the information provided on Form N-CSRS in its regulatory, disclosure review, inspection, and policymaking roles.

A registrant is required to disclose the information specified by Form N-CSRS, and the Commission will make this information public. A registrant is not required to respond to the collection of information contained in Form N-CSRS unless the Form displays a currently valid Office of Management and Budget (“OMB”) control number. Please direct comments concerning the accuracy of the information collection burden estimate and any suggestions for reducing the burden to Secretary, Securities and Exchange Commission, 450 Fifth Street, NW, Washington, DC 20549-0609. The OMB has reviewed this collection of information under the clearance requirements of 44 U.S.C. § 3507.

Item 1.   Certified Financial

Ultra Series Fund | June 30, 2017

Nondeposit investment products are not federally insured, involve investment risk, may lose value and are not obligations of or guaranteed by any financial institution. For more complete information about Ultra Series Fund, including charges and expenses, request a prospectus from your financial advisor or from CMFG Life Insurance Company, 2000 Heritage Way, Waverly, IA 50677.

Consider the investment objectives, risks, and charges and expenses of any fund carefully before investing. The prospectus contains this and other information about the investment company. For more current Ultra Series Fund performance information, please call 1-800-670-3600. Current performance may be lower or higher than the performance data quoted within. Past performance does not guarantee future results. Nothing in this report represents a recommendation of a security by the investment adviser. Portfolio holdings may have changed since the date of this report.

Ultra Series Fund | June 30, 2017

The six-month period end marked the tenth anniversary of the beginning of the Financial Crisis, which ended with risk assets advancing to record levels. The S&P 500^® returned 9.34%, the Russell Midcap^® returned 7.99% and the MSCI EAFE^® advanced 13.81% during the six-month period. Although the Federal Reserve (Fed) again voted to raise short-term interest rates, bond indices advanced as longer-term interest rates fell, and coupled with interest income, produced strong returns. The BofA Merrill Lynch U.S. High Yield Constrained Index advanced 4.90% and the Bloomberg Barclays Aggregate Index gained 2.27% for the six-month period.

June 2007 marked the beginning of events that led to what is now known as the Great Recession, an event that triggered great economic chaos and led to unprecedented central bank intervention. The collapse of two Bear Stearns hedge funds (exposed to sub-prime credit derivatives) in June 2007 marked the start of trouble. By August 2007, the Fed reversed its tightening course as contagion led to disarray in the money-markets and equity markets. By March 2008, Bear Stearns was forced to merge with JP Morgan, and Lehman Brothers was bankrupt by September 2008. Equity markets reached their low point in March 2009 as central-banks engaged in unprecedented monetary stimulus which included not only cutting interest rates (in some cases to negative levels) but also the buying of financial assets (better known as quantitative easing or QE).

Ten years later, investors are happily counting their regained fortunes as central banks now weigh options on how to withdraw the “morphine drip” from the financial markets - which have seemingly become addicted to easy central bank policies (low interest rates, along with unprecedented asset purchases by the central banks). Make no mistake, many of these policies likely prevented a complete collapse of the economic system and a depression-like scenario from occurring. Meanwhile, as investors are feeling no pain, the economy continues to limp along with modest growth (first quarter GDP up 1.4%) and high optimism as asset values continue to stretch. Perhaps, nowhere has this optimism been more apparent than in the Technology sector, with the “Fab Five” (Facebook, Amazon, Apple, Microsoft and Google parent, Alphabet) contributing an outsized portion of the S&P 500 Index’s return during the first half of 2017.

On the economic front, the most positive economic news seems to be “soft” data – sentiment, consumer confidence and other surveys which ask about future intention to spend. Actual “hard” economic data – measureable data based upon actions - has been harder to come by and, in-fact, has been well below expectations. Similar to the past eight years, the data hasn’t been extremely weak, it’s just been weak relative to expectations and presumably what’s priced in the equity market. Although the equity market has been signaling optimism, the bond market has been pricing a very different scenario. Despite the Fed raising short-term interest rates in March and June, the 10-year Treasury yield reached a low of 2.13% in June, its lowest level since November 10, 2016. This flattening of the yield curve (the declining difference between short and long-term interest rates) typically implies that economic expansion is slowing and the “hard” data seems to be confirming it. One plausible explanation for this disconnect is that if we remain in a stable, low-growth, low-inflation environment for an extended period of time, interest rates will remain low and in-turn risk assets (even with lower expected returns) will look attractive compared to bond yields.

This conundrum between the bond and stock market (and between “soft” and “hard” economic data) leads us to believe that the low levels of volatility in the market may not persist. Elevated stock valuations and weakening economic data along with high expectations and high optimism create a recipe for higher volatility in the future. Although lofty valuations (along with stock prices) may continue longer than justified, we believe investors should prepare for more modest returns. With this backdrop we believe stocks of lower-risk, higher-quality companies along with shorter-duration, higher-quality bonds will allow investors to continue to participate in the market, while providing some shelter should volatility return to more typical levels.

Ultra Series Fund | June 30, 2017

ALLOCATION FUNDS SUMMARY

The Ultra Series Conservative Allocation, Moderate Allocation and Aggressive Allocation Funds (the “Funds”) invest primarily in shares of registered investment companies (the “Underlying Funds”). The Funds will be diversified among a number of asset classes and their allocation among Underlying Funds will be based on an asset allocation model developed by Madison Asset Management, LLC (“Madison”), the Funds’ investment adviser. The team may use multiple analytical approaches to determine the appropriate asset allocation, including:

Under normal circumstances, the Ultra Series Conservative Allocation Fund’s total net assets will be allocated among various asset classes and Underlying Funds, including those whose shares trade on a stock exchange (exchange traded funds or “ETFs”), with target allocations over time of approximately 35% equity investments and 65% fixed income investments. Underlying Funds in which the Fund invests may include funds advised by Madison and/or its affiliates, including the Madison Funds (the “Affiliated Underlying Funds”). Generally, Madison will not invest more than 75% of the Fund’s net assets, at the time of purchase, in Affiliated Underlying Funds. Although actual allocations may vary, as of June 30, 2017, the Fund’s asset allocation was:

The Ultra Series Conservative Allocation Fund (Class I) returned 5.19% for the period, outperforming the Conservative Allocation Fund Custom Index return of 5.09%. The Fund lagged its peers as measured by the Morningstar Allocation – 30% to 50% Equity Category, which advanced 5.51%.

Under normal circumstances, the Ultra Series Moderate Allocation Fund’s total net assets will be allocated among various asset classes and Underlying Funds, including those whose shares trade on a stock exchange (exchange traded funds or “ETFs”), with target allocations over time of approximately 60% equity investments and 40% fixed income investments. Underlying Funds in which the Fund invests may include Affiliated Underlying Funds. Generally, Madison will not invest more than 75% of the Fund’s net assets, at the time of purchase, in Affiliated Underlying Funds. Although actual allocations may vary, as of June 30, 2017, the Fund’s asset allocation was:

Ultra Series Fund | Review of Period (unaudited) - continued | June 30, 2017

The Ultra Series Moderate Allocation Fund (Class I) returned 7.22% for the period, beating its blended benchmark, the Moderate Allocation Fund Custom Index, which returned 7.14%. The Fund also beat its Morningstar peer group as the Allocation – 50% to 70% Equity Category, which returned an average of 7.19%.

Under normal circumstances, the Ultra Series Aggressive Allocation Fund’s total net assets will be allocated among various asset classes and Underlying Funds, including those whose shares trade on a stock exchange (exchange traded funds or “ETFs”), with target allocations over time of approximately 80% equity investments and 20% fixed income investments. Underlying Funds in which the Fund invests may include Affiliated Underlying Funds. Generally, Madison will not invest more than 75% of Fund’s net assets, at the time of purchase, in Affiliated Underlying Funds. Although actual allocations may vary, as of June 30, 2017, the Fund’s asset allocation was:

The Ultra Series Aggressive Allocation Fund (Class I) returned 8.82% for the period, beating its blended benchmark, the Aggressive Allocation Fund Custom Index, which returned 8.80%. The Fund outperformed its Morningstar Allocation – 70% to 85% Equity Category peer group, which averaged an 8.60% return.

Under normal circumstances, the Ultra Series Core Bond Fund invests at least 80% of its net assets in bonds. To keep current income relatively stable and to limit share price volatility, the Fund emphasizes investment grade securities and maintains an intermediate (typically 3-7 year) average portfolio duration, with the goal of being between 85-115% of the market benchmark duration. The Fund also strives to add incremental return in the portfolio by making strategic decisions relating to credit risk, sector exposure and yield curve positioning. The Fund may invest in corporate debt securities, U.S. Government debt securities, foreign government debt securities, non-rated debt securities, and asset-backed, mortgage-backed and commercial mortgage-backed securities.

The Ultra Series Core Bond Fund (Class I) returned 2.06% for the period, moderately trailing the Fund’s benchmark, the Bloomberg Barclays U.S. Aggregate Bond Index, which advanced 2.27%. The Morningstar Intermediate-Term Bond peer group gained 2.59% for the period.

The Ultra Series High Income Fund invests primarily in lower-rated, higher-yielding income bearing securities, such as “junk” bonds. Because the performance of these securities has historically been strongly influenced by economic conditions, the Fund may rotate securities selection by business sector according to the economic outlook. Under normal market conditions, the Fund invests at least 80% of its net assets in bonds rated lower than investment grade (BBB/Baa) and their unrated equivalents or other high-yielding securities.

The Ultra Series High Income Fund (Class I) returned 4.29% during the period, lagging the Bank of America Merrill Lynch U.S. High Yield Constrained Index 4.90% return. The Fund

Ultra Series Fund | Review of Period (unaudited) - continued | June 30, 2017

also trailed its Morningstar High Yield Bond category peer group, which returned 4.55%.

† Consumer Discretionary includes securities in the following industries: Advertising; Auto Parts & Equipment; Entertainment; Leisure Time; Lodging; Media and Retail.

The Ultra Series Diversified Income Fund seeks income by investing in a broadly diversified array of securities including bonds, common stocks, real estate securities, foreign market bonds and stocks and money market instruments. Bonds, stock and cash components will vary, reflecting the portfolio managers’ judgments of the relative availability of attractively yielding and priced stocks and bonds; however, under normal market conditions, the Fund’s portfolio managers generally attempt to target a 40% bond and 60% stock investment allocation. Nevertheless, bonds (including investment grade, high yield and mortgage- or asset-backed) may constitute up to 80% of the Fund’s assets, stocks (including common stocks, preferred stocks and convertible bonds) may constitute up to 70% of the Fund’s assets, real estate securities may constitute up to 25% of the Fund’s assets, foreign (including American Depositary Receipts (“ADRs”) and emerging market) stocks and bonds may constitute up to 25% of the Fund’s assets, and money market instruments may constitute up to 25% of the Fund’s assets. Although the Fund is permitted to invest up to 80% of its assets in lower credit quality bonds, under normal circumstances, the Fund intends to limit the investment in lower credit quality bonds to less than 50% of the Fund’s assets. The balance between the two strategies of the Fund (fixed income and equity investing) is determined after reviewing the risks associated with each type of investment, with the goal of meaningful risk reduction as market conditions demand.

The Ultra Series Diversified Income Fund (Class I) advanced 5.14% for the period, lagging its blended index (50% Bank of America Merrill Lynch U.S. Corporate, Government and Mortgage Index and 50% S&P 500^®) which returned 5.81%. The Fund’s designated Morningstar peer group, the Allocation – 50% to 70% Equity category, averaged a 7.19% return for the period.

The Ultra Series Large Cap Value Fund will, under normal market conditions, maintain at least 80% of its net assets in large cap stocks. The Fund follows a “value” approach, meaning the portfolio managers seek to invest in stocks at prices below their perceived intrinsic value as estimated based on fundamental analysis of the issuing company and its prospects. By investing in value stocks, the Fund attempts to limit the downside risk over time but may also produce smaller gains than other stock funds if their intrinsic values are not realized by the market or if growth-oriented investments are favored by investors. The Fund will diversify its holdings among various industries and among companies within those industries.

The Ultra Series Large Cap Value Fund (Class I) returned 4.60% for the period, slightly trailing its benchmark, the Russell 1000^® Value Index, which advanced 4.66%. The

Ultra Series Fund | Review of Period (unaudited) - continued | June 30, 2017

Fund underperformed its Morningstar peer group, Large Value category, which showed a 5.54% return.

†Financials includes securities in the following industries: Capital Markets; Commercial Banks; Diversified Financial Services; and Insurance.

The Ultra Series Large Cap Growth Fund invests primarily in common stocks of larger companies and will, under normal market conditions, maintain at least 80% of its net assets in large cap stocks. Stocks selected for the Fund will represent primarily well-established companies that have a demonstrated pattern of consistent growth. To a lesser extent, the Fund may invest in less established companies that may offer more rapid growth potential. The Fund has an active trading strategy which will lead to more portfolio turnover than a more passively-managed fund.

The Ultra Series Large Cap Growth Fund (Class I) returned 10.99% for the period, trailing its benchmark, the Russell 1000^® Growth Index, which returned 13.99%. The Fund lagged its peer group, Morningstar Large Growth category, which averaged a return of 15.56% over the same period.

†Informatiom Technology includes securities in the following industries: Communications Equipment; Computers & Peripherals; Electronic Equipment, Instruments & Components; Internet Software & Services; IT Services and Software.

The Ultra Series Mid Cap Fund generally invests in common stocks of midsize companies and will, under normal market conditions, maintain at least 80% of its net assets in mid cap securities. The Fund seeks attractive long-term returns through bottom-up security selection based on fundamental analysis in a diversified portfolio of high-quality growth companies with attractive valuations. These will typically be industry leading companies in niches with strong growth prospects. The Fund’s portfolio managers believe in selecting stocks for the Fund that show steady, sustainable growth and reasonable valuations. As a result, stocks of issuers that are believed to have a blend of both value and growth potential will be selected for investment.

The Ultra Series Mid Cap Fund (Class I) returned 5.45% for the period, underperforming its benchmark, the Russell Midcap^® Index, which showed a 7.99% return. The Fund underperformed its peer group, the Morningstar Mid-Cap Growth category, whose average return was 13.77%.

Ultra Series Fund | Review of Period (unaudited) - continued | June 30, 2017

The Ultra Series International Stock Fund will invest, under normal market conditions, at least 80% of its net assets in the stock of foreign companies. Typically, a majority of the Fund’s assets are invested in relatively large cap stocks of companies located or operating in developed countries. The Fund may also invest up to 30% of its assets in securities of companies whose principal business activities are located in emerging market countries. The portfolio managers typically maintain this segment of the Fund’s portfolio in such stocks which it believes have a low market price relative to their perceived value based on fundamental analysis of the issuing company and its prospects. The Fund may also invest in foreign debt and other income bearing securities at times when it believes that income bearing securities have greater capital appreciation potential than equity securities.

The Ultra Series International Stock Fund (Class I) returned 11.82% for the period, trailing the 13.81% return of the MSCI EAFE Index (net). The Fund underperformed its peer group, with the Morningstar Foreign Large Blend Category averaging a 14.58% return.

Ultra Series Fund | Review of Period (unaudited) - continued | June 30, 2017

ALLOCATION FUND CUSTOM INDEXES*

The Conservative Allocation Fund Custom Index consists of 65% Bloomberg Barclays US Aggregate Bond Index, 24.5% Russell 3000^® Index and 10.5% MSCI ACWI ex-USA Index (net). See market index descriptions below.

The Moderate Allocation Fund Custom Index consists of 40% Bloomberg Barclays US Aggregate Bond Index, 42% Russell 3000^® Index and 18% MSCI ACWI ex-USA Index (net). See market index descriptions below.

The Aggressive Allocation Fund Custom Index consists of 20% Bloomberg Barclays US Aggregate Bond Index, 56% Russell 3000^® Index and 24% MSCI ACWI ex-USA Index (net). See market index descriptions below.

HYBRID FUND CUSTOM INDEXES*

The Custom Blended Index consists of 50% S&P 500^® Index and 50% of Bank of America Merrill Lynch U.S. Corporate, Government and Mortgage Index. See market indexes’ descriptions below.

*The Custom Indexes are calculated using a monthly re-balancing frequency (i.e., rebalanced back to original constituent weight every calendar month-end).

MARKET INDEXES

The Bank of America Merrill Lynch U.S. Corporate, Government & Mortgage Index is a broad-based measure of the total rate of return performance of the U.S. investment-grade bond markets. The index is a capitalization-weighted aggregation of outstanding U.S. treasury, agency and supranational mortgage pass-through, and investment-grade corporate bonds meeting specified selection criteria.

The Bank of America Merrill Lynch U.S. High Yield Constrained Index tracks the performance of below investment grade U.S. dollar denominated corporate bonds publicly issued in the U.S. domestic market, but limits any individual issuer to a maximum weighting of 2%.

The Bloomberg Barclays U.S. Aggregate Bond Index is a broad-based flagship benchmark that measures the investment grade, U.S. dollar-denominated, fixed-rate taxable bond market. The index includes Treasuries, government-related and corporate securities, mortgage backed securities, asset backed securities and commercial mortgage-backed securities.

The MSCI EAFE (Europe, Australasia & Far East) Index (net) is a free float-adjusted market capitalization index that is designed to measure developed market equity performance, excluding the U.S. and Canada. The MSCI EAFE Index (net) is calculated on a total return basis with dividends reinvested after the deduction of withholding taxes.

The MSCI ACWI ex USA Index is a free float-adjusted market capitalization weighted index that is designed to measure the equity market performance of developed and emerging markets. The MSCI ACWI ex USA (net) is calculated on a total return basis with dividends reinvested after the deduction of withholding taxes.

The Russell 1000^® Growth Index is a large-cap market index which measures the performance of those Russell 1000 companies with higher price-to-book ratios and higher forecasted growth values.

The Russell 1000^® Value Index is a large-cap market index which measures the performance of those Russell 1000 companies with lower price-to-book ratios and lower forecasted growth values.

The Russell 3000^® Index measures the performance of the 3,000 largest U.S. companies based on total market capitalization, which represents 98% of the investable U.S. equity market.

The Russell Midcap^® Index is a mid-cap market index which measures the performance of the mid-cap segment of the U.S. equity universe.

Ultra Series Fund | Review of Period (unaudited) - concluded | June 30, 2017

The S&P 500^® Index is a large-cap market index which measures the performance of a representative sample of 500 leading companies in leading industries in the U.S.

© Morningstar, Inc. All rights reserved. The information contained herein: (1) is proprietary to Morningstar and/or its content providers; (2) may not be copied or distributed; and (3) is not warranted to be accurate, complete, or timely. Neither Morningstar nor its content providers are responsible for any damages or losses arising from any use of this information.

Past performance is no guarantee of future results.

Russell Investment Group is the source and owner of the trademarks, service marks and copyrights related to the Russell Indexes. Russell^® is a trademark of Russell Investment Group.