The present invention provides a polybutylene terephthalate resin composition which has an excellent vibration welding performance, an excellent resistance to heat shock, and is useful for a case, housing and the like of electric/electronic parts. Specifically, it provides a polybutylene terephthalate resin composition for vibration welding comprising (A) 100 parts by weight of a polybutylene terephthalate resin; (B) 20 to 100 parts by weight of a modified polyester copolymer containing 5 to 30% by mole of a comonomer; (C) 5 to 30 parts by weight of an elastomer selected from an acrylic-based copolymer having a glycidyl group and/or an α-olefin.α,β-unsaturated carboxylic acid (ester).α,β-unsaturated carboxylic acid glycidylester-based ternary polymer; and (D) 60 to 150 parts by weight of a glass fiber.