Thermoplastic resin compositions are provided. A heat-resistant ABS thermoplastic resin composition including a graft ABS polymer, an .alpha.-methylstyrene copolymer, an imide-substituted copolymer, and an additive for improving elongation and impact strength is excellent in weld strength, chemical resistance, impact strength, and elongation. A thermoplastic resin composition including a graft ABS polymer, a .alpha.-methylstyrene copolymer, and an additive for improving wettability is excellent in weld strength and wettability.