Methods are provided for surface-modifying a rubber vulcanizate or a thermoplastic elastomer. The methods allow these rubber vulcanizate or thermoplastic elastomer objects to have a lubricating surface layer chemically fixed thereon, instead of having a resin coating which has drawbacks such as a reduction in lubricity due to e.g. separation or peeling of the coating during movement within a vessel or tract. The present invention relates to a method for surface-modifying an object made of a rubber vulcanizate or a thermoplastic elastomer, the method including: step 1 of forming polymerization initiation points on a surface of the object； and step 2 of radically polymerizing a monomer starting from the polymerization initiation points by irradiation with ultraviolet light having a wavelength of 300 to 400 nm in the presence of an alkali metal salt to grow polymer chains on the surface of the object.
