A thermoplastic composition which comprises a blend comprising 20 to 80% by weight of a polycarbonate resin and 80 to 20% by weight of a graft polymer obtained by grafting at least one aromatic vinyl compound and at least one of vinyl cyanides and alkyl unsaturated carboxylates onto a conjugated diene rubber or its mixture with a copolymer of at least one aromatic vinyl compound and at least one of vinyl cyanides and alky unsaturated carboxylates in an amount of not more than 90% by weight on the basis of the combined amount of the graft polymer and the copolymer, and a polyolefin or a plasticizer having a light transmission of not less than 70% when determined on the film of 20 microns in thickness prepared by the use of a solution of the plasticizer (0.25 g) and acrylonitrile-styrene copolymer (weight ratio of acrylonitrile and styrene, 30:70; 0.75 g) in acetone (10 ml), the weight proportion of the blend and the polyolefin or the plasticizer being 100:0.2-20. The resulting composition is excellent in solvent resistance, welding strength, impact resistance, molding property, etc.