Disclosed is a composition for treating a metal surface, which enables the formation of a coating film that can impart excellent corrosion resistance and excellent coating film appearance to a metallic material, particularly a metal structure having complex geometry. Specifically disclosed is a composition for treating a metal surface, which comprises 5 to 30 wt% of an aqueous resin, 100 to 5000 ppm of a trivalent Bi ion, and an amino polycarboxylic acid at a 0.1- to 5-fold molar concentration relative to the concentration of the Bi ion. The composition is characterized in that at least a part of the aqueous resin comprises a nonionic and/or cationic resin represented by formula (1) [wherein R1 and R2 independently represent a group represented by the formula: -(R)m-X (wherein R represents an alkylene group having 1 to 6 carbon atoms; m represents 1 or 0; and X represents a hydrogen atom, a carboxyl group, a hydroxyl group, or an acyl group)] and containing, in the polymer skeleton thereof, a nitrogenated group capable of being bound to the Bi ion to form a chelate.
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