An object of the present invention is to provide a production method which can increase the activity of a catalyst particle comprising a core particle and an outermost layer, the core particle comprising at least one of palladium and a palladium alloy, and the outermost layer comprising at least one of platinum and a platinum alloy and covering the core particle. The method is for producing a catalyst for fuel cells, in which a catalyst particle is supported by an electroconductive carrier, the method comprising the steps of: preparing a supported catalyst in which a catalyst particle comprising a core particle and an outermost layer is supported by an electroconductive carrier, the core particle comprising at least one of palladium and a palladium alloy, and the outermost layer comprising at least one of platinum and a platinum alloy and covering the core particle; acid treatment to bring the supported catalyst into contact with an acid solution which dissolves palladium more preferentially than platinum; and firing the supported catalyst at 80° C. or more and less than 200° C. in a reducing gas atmosphere after the acid treatment step.