To maintain a rust preventing effect for many days, to rapidly produce the effect and to prevent the reduction of the effect even after dew condensation by mixing a rust preventing oil with a volatile corrosion inhibitor mixed with an alcohol soln.

A rust preventing oil is mixed with a volatile corrosion inhibitor based on N-cyclohexyl-cyclohexylamine, etc., and mixed with a soln. of an alcohol such as n-propanol to obtain the objective volatile rust preventing liq. A non-oil rust preventing soln. such as water is added to the corrosion inhibitor if necessary. The volatile rust preventing liq. is applied or sprayed on the surface of a metallic product to coat the surface with the components of the rust preventing liq. in the form of a film. The volatile corrosion inhibitor volatilizes and rapidly produces its rust preventing effect after sticking to the surface. Since the rust preventing oil and the unvolatilized volatile corrosion inhibitor in the film coat the surface, the rust preventing effect can be maintained for an increased number of days.