The present invention features a method for preparing a PtCo nanocube catalyst, the method comprising dissolving a platinum (Pt) precursor, a cobalt (Co) precursor, a surface stabilizer and a reducing agent in a solvent to prepare a solution; heating the solution under an inert gas atmosphere; maintaining the temperature of the solution to obtain PtCo alloy nanocubes; adsorbing the PtCo alloy nanocubes on a carbon support to obtain a catalyst; and removing the surface stabilizer from the catalyst. The disclosed method for preparing a PtCo nanocube catalyst enables preparation of nanocubes with uniform size and cubic shape through a simple process and application for development of high-efficiency fuel cells by preventing change in shape, surface area and composition caused by agglomeration of the nanocubes.