Disclosed is a surface-treating agent for oil seal lip portion, comprising a lubricant filler and an adduct compound consisting of an adduct of toluene diisocyanate and trimethylolpropane, the surface-treating agent being applied to the surface of vulcanized rubber forming a lip portion of an oil seal comprising the lip portion and a metal ring. The application of the surface-treating agent of the present invention to the sliding surface of a seal lip portion of an oil seal effectively lengthens the service life of the oil seal, when used in a sliding part or a moving part, and leads to energy saving of equipment that uses the oil seal.
