PURPOSE: To obtain a rubber stopper for sealing purpose, which has excellent lubricity and a high fouling resistance against bacteria, etc., by forming on its surface a vulcanized fluorine-containing elastomer film composed of a graft copolymer containing a fluorine-containing polymer segment and an organopolysiloxane segment.

CONSTITUTION: A rubbery elastic graft copolymer is obtained by chemically and alternately combining 100pts.wt. a fluorine-containing polymer segment (a) of a number-average polymerization degree of 50W10,000 with 1W2,000pts.wt. an organopolysiloxane segment (b) of a number-average polymerization degree of 50W50,000 through reaction sites contained in the segment molecules. Then, the vulcanized film of the fluorine-containing elastomer composed of the graft copolymer thus obtained is coated on part or whole of the surface of a sealing rubber stopper for a parenteral injection bottle, etc., to obtain the objective rubber stopper.