A thermoplastic resin composition having improved heat stability which comprises a thermoplastic resin which contains at least 5 % by weight of an alpha -alkyl-substituted aromatic copolymer comprising alpha -alkyl-substituted aromatic vinyl compound and at least one other comonomer copolymerizable therewith, wherein the composition contains a metal-deactivating agent which has a molecular weight of not more than 2,000 and at least one group of the formula: <CHEM> or an organometallic colorant containing free metal in an amount of not more than 2,000 ppm, from which a molded article having no or less silver streaks can be produced.
