A thermoplastic resin composition superior in heat stability and impact resistance, which comprises 95-5% by weight of a thermoplastic polymer (A) selected from homopolymers and copolymers of ethylenic unsaturated monomers or from polymers of bifunctionally reactive compounds and 5-95% by weight of a compound-rubber-based graft copolymer which is produced by the graft polymerization of one or more vinyl monomers onto compound rubber particles having an average diameter of 0.08-0.6 .mu.m and structures in which 10-90% by weight of a polyorganosiloxane rubber component and 90-10% by weight of a polyalkyl(meth)acrylate rubber component are tangled together so as not to be separable from each other.