Provided are surface-modified objects, preferably elastic bodies (e.g. gasket for syringes) each obtained by a surface modification method for modifying a rubber vulcanizate or a thermoplastic elastomer, the method being capable of providing surfaces with excellent properties such as excellent sliding properties, excellent durability against repeated sliding motion, and excellent performance in preventing adsorption and aggregation of proteins, and allowing the surfaces to maintain the sealing properties, without using expensive self-lubricating plastics. The invention relates to surface-modified objects, preferably elastic bodies (e.g. gasket for syringes) at least partially having a surface modified by a surface modification method including: step 1 of forming polymerization initiation points on a surface of an object to be modified that includes a rubber vulcanizate or thermoplastic elastomer, and step 2 of radically polymerizing a monomer containing a C-N bond in a molecule thereof, starting from the polymerization initiation points, to grow polymer chains on the surface of the object.