PROBLEM TO BE SOLVED: To provide a surface modification method for a vulcanized rubber or a thermoplastic elastomer that not only gives excellent slidability and durability against repetition of sliding but also can improve the sealability without using an expensive resin having self-lubricity, and to provide a surface-modified elastic body such as a gasket for a syringe and a catheter having at least partially a modified surface obtained by the surface modification method, and a tire having at least partially a surface of grooves, modified by the surface modification method, in the tire.SOLUTION: The surface modification method for a vulcanized rubber or a thermoplastic elastomer as an object to be modified includes: a step 1 of forming polymerization initiation points on a surface 13 of the object to be modified a step 2 of radically polymerizing a monomer, starting from the polymerization initiation points to grow a polymer chain on the surface 13 of the object to be modified and a step 3 of irradiating the grown polymer chain with ultraviolet rays.
