Abstract: A surface-blackened steel sheet is produced by electrolyzing a steel sheet at a cathode in an acidic aqueous solution containing Zn.sup.2+, at least one of Fe.sup.2+, Co.sup.2+ and Ni.sup.2+, a film-improving ion consisting of at least one member selected from the group consisting of Cr.sup.3+, Fe.sup.2+, Pb.sup.2+, In.sup.2+, Ag.sup.2+, Sn.sup.2+, Ti.sup.2+, Al.sup.3+, Cu.sup.2+, Mo.sup.6+, V.sup.3+, V.sup.6+, Mn.sup.2+, Mn.sup.4+, Mn.sup.6+, Bi.sup.2+, sulfite ion, thiosulfate ion, thiocyanate ion, sulfamate ion and sulfonate ion, an oxidizing ion and an organic hydroxy-compound as main components, thereby forming a black film on the steel sheet, followed by water washing, a chromate treatment, if required, and coating with a guard coat.