Provided are methods for surface-modifying a tubular object of a rubber vulcanizate or a thermoplastic elastomer. The methods allow these objects to have at least a lubricating inner surface layer chemically fixed thereon, instead of having a resin coating which has drawbacks such as reduction in lubricity due to e.g. separation or peeling of the coating during movement within a vessel or tract. Included is a method for surface-modifying a tubular object made of a rubber vulcanizate or a thermoplastic elastomer whose side wall may have an opening, the method including: step 1 of forming polymerization initiation points on at least the outer surface of the object and step 2 of irradiating the outer surface of the object with ultraviolet light of 300-400 nm to radically polymerize a monomer using radicals generated from the polymerization initiation points to grow polymer chains on at least the inner surface of the object.
