The thermoplastic resin composition according to the present invention comprises (A) about 20.about.95 parts by weight of a rubber-modified polystyrene resin composed of (a.sub.1) about 10.about.60% by weight of a styrene-containing graft copolymer resin containing about 10.about.60% by weight of a rubber and about 90.about.40% by weight of a styrene-acrylonitrile copolymer, the styrene-acrylonitrile copolymer containing about 0.5.about.10% by weight of acrylonitrile, and (a.sub.2) about 90.about.40% by weight of a styrene-containing copolymer resin containing 0.about.20% by weight of a rubber; and (B) about 5.about.80 parts by weight of a polyphenylene ether.