Provided are methods for surface-modifying a rubber vulcanizate or a thermoplastic elastomer, which enable surfaces with a chemically fixed lubricant to be produced instead of a resin coating which has drawbacks, such as that lubricity is reduced due to separation, peeling or the like of the coating during the 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 halogen-containing deliquescent monomer, starting from the polymerization initiation points, by irradiation with ultraviolet light having a wavelength within the range of 300 to 400 nm to grow polymer chains on the surface of the object.