A thermoplastic resin composition which comprises (A) a styrene resin and/or polyphenylene ether resin, (B) an olefin resin, and (C) a partially hydrogenated block copolymer, the ingredient (C) being contained in an amount of 2 to 30 parts by weight per 100 parts by weight of the sum of the ingredients (A) and (B), wherein the ingredient (C) is a partially hydrogenated block copolymer obtained from a block copolymer which has a polymer block (X) consisting mainly of units of a vinylaromatic compound and a polymer block (Y) consisting mainly of units of a conjugated diene compound and has a combined vinylaromatic content of 30 to 80 wt.% and a combined vinyl content in the polymer block (Y) of 20 to 65 wt.%, excluding 65 wt.%, by hydrogenating 35 to 70%, excluding 70%, of the double bonds attributable to the conjugated diene compound in the polymer block (Y). It is satisfactory in heat resistance, oil resistance, and thermal aging resistance.
