Abstract: A chromate treatment bath composition, afforded by the introduction, into an aqueous solution containing hexavalent Cr ions and trivalent Cr ions, of a nonionic-anionic composite surfactant that has an anionic moiety and a nonionic moiety composed of a polyethylene glycol group or a group consiting of an ethylene oxide addition polymer, provides metal surfaces onto which a layer of the composition containing 5 to 150 mg/m.sup.2 of total chromium is dried with a chromate film that has an excellent alkali resistance and water resistance, a high chromium fixing ratio, an excellent corrosion resistance, and an excellent paint film adherence.