PURPOSE: To obtain a flame-retardant resin compsn. improved in thermal stability, heat resistance and flame retardancy by adding a graft copolymer prepd. by grafting silicone and acrylic rubbery polymers with a vinyl compd. to a resin compsn.

CONSTITUTION: 100 pts.wt. resin compsn. comprising (A) 10-80 pts.- wt. graft copolymer of 10-70wt.%. graft component composed of a vinyl cyanide compd. and an arom. vinyl compd. at a wt. ratio of 0.2 to 4.0 and 30-90wt.% rubbery polymer, (B) 0-90 pts.wt. vinyl copolymer of a vinyl cyanide compd. and an arom. vinyl compd. at a wt. ratio of 0.2 to 0.4, and (C) 0-80 pts.wt. copolymer of a vinyl cyanide compd. and/or an arom. vinyl compd. with 5-60wt.% maleimide compd. and/or an arom. vinyl compd. with (D) 8-30 pts.wt. halogen-contg. compd. of the formula (wherein X is bromine or chlorine; (a) to (d) are each 1 to 4; and (n) is 0 or a natural no.) or the like, and (E) 0.01-10 pts. wt. graft copolymer of a composite rubber of a silicone rubber and an acrylic rubber with a vinyl compd.