Abstract: A treating solution for a gold- or gold-alloy-plated material having nickel or a nickel-containing alloy as an underplating on a metallic material, the solution including a particular inhibitor, such as benzotriazole, a lubricant containing a particular fatty acid, and an emulsifier containing a particular alkyl phosphate. Treating is performed by coating the gold or gold-alloy-plated material with the treating solution or by electrolyzing in the treating solution using the gold-plated material as an anode.