Exhibit 23 CONSENT OF INDEPENDENT AUDITORS We consent to the incorporation by reference in the Registration Statements on Form S-3 (Nos. 333-70761, 333-29483, 333-88532 and 333-105092) and on Form S-8 (Nos. 333-69895, 333-87413, 333-42942, 333-42944, 333-73738, 333-73740, 333-88398, 333-91906 and 333-97987) of Ohio Casualty Corporation and subsidiaries of our report dated February 12, 2004, with respect to the financial statements and schedules of Ohio Casualty Corporation and subsidiaries included in the Annual Report to Shareholders on Form 10-K for the years ended December 31, 2003, 2002 and 2001. /s/ Ernst & Young LLP Ernst & Young LLP Cincinnati, Ohio March 10, 2004