PURPOSE: A polybutylene terephthalate composition that is composed of polybutylene terphthalate, a specific amount of fiberglass and talc, thus being useful as engineering plastics becaue it has high heat resistance and mechanical properties, causing reduced warpage.

CONSTITUTION: Said composition comprises (A) polybutylene terephthalate, (B) glass fibers, and (C) talc, in which when each content is exhibited as x, y and z in wt% for A, B and C respectively, 50≤x≤75.3≤y≤15,y+15≤Z<40, preferably x is 60W70, y is 25W30.