The present invention provides a method for surface-modifying a rubber vulcanizate or a thermoplastic elastomer, which can cost-effectively provide a variety of functions, such as remarkable sliding properties or biocompatibility, according to the application. The present invention relates to a method for surface-modifying a rubber vulcanizate or a thermoplastic elastomer as a modification target, the method including: step 1 of forming polymerization initiation points A on a surface of the modification target; step 2 of radically polymerizing a non-functional monomer starting from the polymerization initiation points A to grow non-functional polymer chains; step 3 of washing the modification target on which the non-functional polymer chains are grown; step 4 of forming polymerization initiation points B on a surface of the non-functional polymer chains; and step 5 of radically polymerizing a fluorine-containing functional monomer starting from the polymerization initiation points B to grow fluorine-containing functional polymer chains.