A resin composition suitable as an impact modifier for thermoplastic resins, which has an excellent blocking resistance improved without lowering the effect of improving the impact resistance and which comprises 100 parts by weight of a graft copolymer containing a hollow rubber component and at least two additives selected from the group consisting of 0.1 to 10 parts by weight of a higher fatter acid soap, 0.1 to 10 parts by weight of a crosslinked polymer of 0.1 to 100% by weight of a crosslinking monomer and 0 to 99.9% by weight of a vinyl monomer and 0.001 to 5 parts by weight of a silicone oil.