The present invention provides a thermoplastic resin composition characterized by (1) having an excellent appearance even when it is extruded into a molded piece at a high output, (2) retaining its impact strength even after heat exposure, and (3) having less foreign matter generation at the time of production. According to the present invention, in a composition comprising a polyamide, a polyphenylene ether and a block copolymer, a mixture of a block copolymer having a number average molecular weight of less than 120,000 and a block copolymer having a number average molecular weight of 120,000 or more is used as the block copolymer.