PURPOSE: To obtain the title thermoplastic resin composition of excellent heat resistance by mixing a flame-retardant thermoplastic resin with a non-flame- retardant polymeric compound and an inorganic phosphorus compound.

CONSTITUTION: The composition comprises a flame-retardant thermoplastic resin (A), a non-flame-retardant high molecular compound (B) selected from a non-flame-retardant thermoplastic resin and a non-flame-retardant elastomer and an inorganic phosphorus compound (C) selected from among a phosphorus oxide, a phosphoric acid and an ammonium salt of a phosphoric acid in an amount effective for flame retardancy and optionally a filler (D). This composition may further contain a compatibilizer (E) in order to enhance the compatibility of resin A with the compound B. A desirable example of the compatibilizer is a polyisocyanate. Desirable examples of resin A include polyphenylene sulfide and poly(oxy-phenylene/sulfonyl-phenylene). An example of resin B is a polyphenylene ether resin.