The present invention aims to provide a method for surface-modifying a rubber vulcanizate or a thermoplastic elastomer, which is capable of cost-effectively imparting a variety of functions, such as sliding properties and biocompatibility, according to the applications. The present invention relates to a surface modification method for surface-modifying an object of a rubber vulcanizate or a thermoplastic elastomer, the method including: step 1 of forming polymerization initiation points A on a surface of the object 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 forming polymerization initiation points B on the surface of the object where the non-functional polymer chains are formed and step 4 of radically polymerizing a functional monomer, starting from the polymerization initiation points B, to grow functional polymer chains.
