The present invention aims to provide a surface modification method for a rubber vulcanizate or a thermoplastic elastomer, which can impart various functions such as sliding properties and biocompatibility according to its use. The present invention relates to a surface modification method for modifying a rubber vulcanizate or a thermoplastic elastomer as an object to be modified, the method including: Step 1 of forming polymerization initiation points on a surface of the object to be modified; Step 2 of radical polymerizing monomers starting from the polymerization initiation points to grow polymer chains on the surface of the object to be modified; and Step 3 of functionalizing the polymer chains.