A rust preventive oil composition is provided, which includes: (A) a base oil that is at least one oil selected from a mineral oil and a synthetic oil; (B) 0.1 to 10% by mass of water based on a total mass of the composition; and (C) one or more specific rust preventive additives selected from the group consisting of a sarcosine-type compound, a nonionic surfactant, a sulfonate salt, an ester, an amine, a carboxylic acid, a fatty acid amine salt, a carboxylate salt, paraffin wax, a salt of oxidized wax, and a boron compound, wherein the rust preventive oil composition has a kinetic viscosity of 20 to 100 mm2/s at 40° C. The rust preventive oil composition can suppress rust development over a long period of time even when there remains a rust-causing agent, which adheres to the metal parts assembled by bare hands, such as steel sheets, bearings, steel balls, and guide rails.