A gold-cobalt based amorphous alloy plated film consisting of a homogeneous amorphous phase not having microcrystals is formed by electroplating conducted by use of an electroplating bath containing a gold cyanide salt in a concentration of 0.01 to 0.1 mol/dm.sup.3 in terms of gold, a cobalt salt in a concentration of 0.02 to 0.2 mol/dm.sup.3 in terms of cobalt, and a tungstate in a concentration of 0.1 to 0.5 mol/dm.sup.3 in terms of tungsten. The gold-cobalt based amorphous alloy plated film obtained consists of a homogeneous amorphous phase not having microcrystals, and has an enhanced hardness while retaining the good contact resistance and chemical stability intrinsic of gold on such levels as to be free of problems on a practical use basis; therefore, the gold-cobalt based amorphous alloy plated film is effective for use as a contact material in electric and electronic component parts such as relays.