To provide a copper-tin-zinc alloy electroplating bath having excellent productivity, which can form a uniform, glossy copper-tin-zinc alloy plating film with the objective composition even at a current density higher than heretofore without using cyanide compounds, and to provide a method for producing an alloy plating film using the same.

The copper-tin-zinc alloy electroplating bath contains at least one selected from copper salts, tin salts, zinc salts, the alkali metal salts of pyrophosphoric acids, amino acids and the salts thereof, and at least one selected from the hydroxides of alkali metals and the hydroxides of alkaline-earth metals. The bath preferably has the pH of 10 to 14. Further, the total of copper ions, tin ions and zinc ions is preferably 0.03 to 0.3 mol/L, and further, the concentration of the amino acid(s) or the salt(s) thereof is preferably 0.08 to 0.22 mol/L.