PURPOSE: To obtain titled composition of markedly improved notched impact strength, with stable melt viscosity, by incorporating a thermoplastic polyester resin with a polyepoxy compound and an unsaturated carboxylic acid (anhydride)-graft polymerized ethylene-α-olefin copolymer.

CONSTITUTION: The objective composition can be obtained by incorporating, in a molten state. (A) 90W50pts.wt. of a thermoplastic polyester resin (e.g., polybutylene terephthalate, polyethylene terephthalate) with (B) 5W50pts.wt. of a copolymer from a C3W6 α-olefin and 0.01W10(pref. 0.1W7)wt% of unsaturated carboxylic acid(anhydride)-graft polymerized ethylene, and (C) 0.1W10pts.wt., based on 100pts.wt. of the components (A) plus (B), of polyepoxy compound.