PURPOSE: To obtain a thermoplastic resin compsn. which is excellent in heat resistance, impact strength, tensile strength, and mold release characteristics and does not become light-colored even when kept standing at a high temp. and then returned to room temp. by compounding a thermoplastic resin compsn. with a specific compd.

CONSTITUTION: 20-90wt.% thermoplastic copolymer comprising 30-70wt.% arom. vinyl compd. units, 5-50wt.% vinyl cyanide units, and 20-50wt.% N-substd. maleimide units is compounded with 10-80wt.% thermoplastic graft copolymer compsn. which comprises a copolymer consisting of the arom. vinyl comd. units and the vinyl cyanide units and a graft copolymer obtd. by grafting the arom. vinyl compd. and the vinyl cyanide compd. onto a rubber component having a glass transition point of 25°C or lower and has a content of the rubber component of 10-70wt.%, a content of the arom. vinyl units of 40-90wt.%, and a content of the vinyl cyanide units of 10-60wt.%, giving a thermoplastic resin compsn. having a content of the maleimide units of 5-25wt.%, a content of the rubber component of 5-25wt.%, and a grafting ratio of 40-80wt.%. 100 pts.wt. the resulting compsn. is compounded with 0.05-1.5 pts.wt. compd. of the formula (wherein R1 is 2-14C alkyl; R2 and R3 are each 1-6C alkyl; and R4 and R5 are each 8-21C alkyl).