The invention concerns a method of conserving biological prostheses, wherein the method includes the following steps: (a) treating biological prostheses with a solution which contains a mixture of epoxide compounds which are at least in part of different lengths; (b) treating the biological prosthesis treated in accordance with step (a) with an antithrombotic-bearing solution; and (c) possibly storing the prosthesis treated in accordance with step (b) in a sterilising solution. The invention further concerns a biological prosthesis produced in accordance with the method of the invention and a conserving agent.