Abstract: A polyester resin composition obtained by melt-mixing a mixture comprising resin components comprising as main resins(A) a thermoplastic polyester resin and(B) a polyorganosiloxane graft copolymer obtained by graft-polymerizing one or more kinds of vinyl monomer containing at least an epoxy group-containing vinyl monomer onto a compound rubber in which a polyorgano-siloxane rubber and a polyalkyl (meth)acrylate rubber have been inseparably united with each other. According to the present invention is provided a polyester resin composition in which the impact resistance of a thermoplastic polyester resin, a main constituent, has been improved over a wide temperature range including low temperatures below 0.degree. C., and which provides molded products having good appearance.