A method for activating a direct oxidation fuel cell including an anode, a cathode, and a proton-conductive electrolyte membrane interposed between the anode and the cathode is provided. The anode and the cathode each have a catalyst layer on a face in contact with the proton-conductive electrolyte membrane. This method activates the fuel cell by passing a current through the fuel cell from an external power source, with the positive electrode and the negative electrode of the external power source connected to the anode and the cathode of the fuel cell, respectively, while supplying an organic fuel and an inert gas to the anode and the cathode, respectively.