PURPOSE: To provide the titled compsn. which has excellent melt thermal stability and thermal and mechanical properties and does not cause the bleedout of flame retarder, consisting of a specified modified polyethylene terephthalate, a reinforcing filler, an aliph. polyester and a modified brominated epoxy resin.

CONSTITUTION: 35W85wt% polyethylene terephthalate (A) modified by adding 0.1W5wt% compd. of formula I or II (wherein M, M' are each an alkali metal; n, m are each 1 or 2) before the completion of polymn., 5W60wt% reinforcing filler (B) such as glass fiber, 1W10wt% aliph. polyester (C) having an acid value of 1.0 or below and an MW of 4,000 or above obtd. by reacting an aliph. dibasic acid such as succinic acid with a 2W8C glycol such as ethylene glycol, and 5W 30wt% modified brominated epoxy resin (D) obtd. by adding a compd. of formula IV to a compd. of formula III (wherein X is Br; n is a degree of polymn. and 0 or greater), are blended together.