EXHIBIT 5.1 BLAKE DAWSON WALDRON Level 32 Exchange Plaza LAWYERS 2 The Esplanade Perth WA 6000 - ------------------------------ www.bdw.com Tel + 61 8 9366 8000 Fax + 61 8 9366 8111 DX 169 Perth PO Box 7438 Cloisters Square Perth WA 6850 Australia PARTNER pSivida Limited Roger Davies Level 12, BGC Centre Telephone (08) 9366 8022 28 The Esplanade PERTH WA 6000 CONTACT Alan Gibson Telephone (08) 9366 8722 OUR REFERENCE DRD:AJG:09 1395 3581 28 June 2006 Dear Sirs REGISTRATION STATEMENT OF FORM F-3 (SUBORDINATED CONVERTIBLE NOTE) We have acted as Australian legal advisers to pSivida Limited (COMPANY) in connection with the Company's registration statement on Form F-3 (REGISTRATION STATEMENT), originally filed on March 28, 2006 with the Securities and Exchange Commission under the U.S. Securities Act of 1933 as amended (SECURITIES ACT). The Registration Statement relates to the sale by the selling security holder named in it of up to 57,631,650 ordinary shares of the Company represented by 5,763,165 American Depositary Shares that may be issued in connection with a subordinated convertible note and warrant issued by the Company (ISSUE). We are furnishing this opinion as exhibit 5.1 to the Registration Statement, subject to the final paragraph of this opinion. 1. DEFINITIONS In this opinion: (a) ACN means Australian Company Number. (b) ASIC means the Australian Securities and Investments Commission. (c) ASX means Australian Stock Exchange Limited ACN 008 624 691. (d) COMPANY means pSivida Limited, registered in Western Australia, ACN 009 232 026. (e) CONVERTIBLE NOTE means the subordinated convertible promissory note issued by the Company on 16 November 2005 and described in the section headed "The Offering" in the Registration Statement. (f) CORPORATIONS ACT means the Corporations Act 2001 (Cth). PERTH SYDNEY MELBOURNE BRISBANE CANBERRA LONDON PORT MORESBY JAKARTA SHANGHAI BLAKE DAWSON WALDRON 28 June 2006 pSivida Limited Page 2 (g) RELEVANT JURISDICTION means the State of Western Australia, Australia. (h) RELEVANT LAWS means the laws of the Relevant Jurisdiction and the federal laws of Australia as they apply in the Relevant Jurisdiction. (i) SELLING SECURITY HOLDER has the same meaning as in the Registration Statement. (j) WARRANT means the warrant to purchase American Depositary Shares issued by the Company on 16 November 2005 and described in the section headed "The Offering" in the Registration Statement. In this opinion, headings are for convenience only and do not affect interpretation and references to paragraphs are to paragraphs of this opinion. 2. DOCUMENTS REVIEWED For the purposes of giving this opinion, we have examined the following documents: (a) a search of the ASIC database in respect of the Company on 28 June 2006 which shows that the Company is registered; (b) the current constitution of the Company; (c) minutes of the meetings of the board of directors of the Company held on 26 October 2005 and 14 November 2005; (d) minutes of shareholders' meeting dated 15 November 2005; and (e) the Registration Statement. 3. SCOPE This opinion relates only to the Relevant Laws in force at 9.00 am (Western Australian time) on the date of this opinion. This opinion is given on the basis that it will be construed in accordance with the Relevant Laws. 4. OPINION Subject to the assumptions and qualifications set out below, we are of the following opinion: (a) the Company has been duly incorporated and is registered as a public company limited by shares under the Corporations Act; (b) the ordinary shares underlying the American Depository Shares that may be issued: BLAKE DAWSON WALDRON 28 June 2006 pSivida Limited Page 3 (i) on conversion of the Convertible Note; (ii) as interest on the Convertible Note; and (iii) upon exercise of the Warrant will, if issued and paid for as contemplated in the Registration Statement, be legally issued and allotted and fully paid at the time of issue. 5. ASSUMPTIONS For the purposes of this opinion, we have assumed that: (a) if we have reviewed a draft of a document rather than a signed or executed copy, the document will be executed in the form of that draft; (b) the minutes referred to in paragraphs 2(c) and 2(d) accurately reflect the business transacted at those meetings; (c) no party has contravened or will contravene Chapter 2E (Related party transactions) of the Corporations Act or ASX Listing Rule 10 (Transactions with persons in a position of influence) in connection with the Issue; (d) no party has contravened or will contravene section 260A (Financial assistance for acquiring shares) of the Corporations Act in connection with the Issue; (e) the Company was solvent at the time of and immediately after the Issue and is solvent at the date of this opinion; (f) the meetings of the Company's board of directors and shareholders to approve the issue of the Convertible Note and the Warrant (and ordinary shares that may be issued in connection with the Convertible Note and the Warrant) were properly convened and: (i) the resolutions set out in the minutes referred to in paragraphs 2(c) and 2(d) above were properly passed as valid decisions of the board of directors of the Company or the Company's shareholders (as the case may be) and have not been subsequently revoked, cancelled or varied; and (ii) the directors of the Company have properly performed their duties and all provisions relating to the declaration of interest and voting were duly observed; (g) where any obligation in connection with the Issue is to be performed in any jurisdiction other than the Relevant Jurisdiction, its performance will not be illegal or unenforceable under the laws of that jurisdiction; BLAKE DAWSON WALDRON 28 June 2006 pSivida Limited Page 4 We have not investigated whether the assumptions in this paragraph 5 are correct. None of the assumptions is limited by reference to any other assumption. 6. QUALIFICATIONS Our opinion is subject to the following qualifications. 6.1 SEARCHES We have not made any independent investigations or searches, other than requests to ASIC for the company search referred to in paragraph 2(a) (the information disclosed in the search results rely on information lodged by the Company, and the search results may not be complete, accurate or up to date). 6.2 GENERAL QUALIFICATIONS (a) We have relied, as to certain matters of fact, on information provided by officers of the Company. (b) This opinion only relates to the laws of the Relevant Jurisdiction. We express no opinion on laws other than the Relevant Laws. None of the qualifications is limited by reference to any other qualification. 7. CONSENT We hereby consent to the use of this opinion in, and the filing hereof, as an exhibit to the Registration Statement and to the reference to our firm under the heading "Legal Matters" and elsewhere in the prospectus included in the Registration Statement. In giving such consent, we do not thereby admit that we come within the category of persons whose consent is required under Section 7 of the U.S. Securities Act of 1933, as amended, or the Rules and Regulations of the Commission thereunder. Yours faithfully /s/ Blake Dawson Waldron