A method for manufacturing a fuel cell assembly includes: arranging an end face of a gas diffusion layer on a placement jig in a state abutting an end face of a resin frame; melting a part of the frame member and causing to penetrate into the gas diffusion layer by pressurizing the projecting part by way of a heat-transfer member, and heating the projecting part via the heat-transfer member by abutting a heating member against of the heat-transfer member; and solidifying the part of the resin frame having penetrated into the gas diffusion layer, in which an abutting position of the heating member relative to the heat transfer member is set in the melting step so that a central axis of the heating member is positioned more to a side of the gas diffusion layer than the central axis of the projecting part.