A rust preventive oil composition comprising a nonionic surfactant with a hydrophilic-lipophilic index of 10-12 at 0.1-10% by mass based on the total amount of the composition, and at least one rust-preventing additive selected from among sarcosine compounds, sulfonic acid salts, esters, amines, carboxylic acids, fatty acid amine salts, carboxylic acid salts, paraffin waxes, oxidized wax salts, alkyl or alkenylsuccinic acid derivatives and boron compounds, the composition having a 40° C. kinematic viscosity of 1-50 mm2/s.