Exhibit 21 Ohio Casualty Corporation Subsidiaries of Registrant as of December 31, 2003 Name of Subsidiary State of Incorporation The Ohio Casualty Insurance Company Ohio West American Insurance Company Indiana Ohio Casualty of New Jersey, Inc. Ohio Ohio Security Insurance Company Ohio American Fire and Casualty Company Ohio Avomark Insurance Company Indiana Ocasco Budget, Inc. Ohio Avomark Insurance Agency, LLC Ohio Ohio Life Brokerage Services, Inc. Kentucky OCI Printing, Inc. Ohio Ocasco Securities Corporation Ohio