PURPOSE: The titled composition which has excellent melt-flow characteristics, heat resistance (stability), and impact resistance, which comprises a specified graft copolymer and a polyphenylene ether resin.

CONSTITUTION: A graft copolymer (A) is obtained by the graft polymerization of an alkenyl aromatic monomer (e.g. styrene) and 3W20pts.wt. unsaturated α,β- dicarboxylic anhydride (e.g. maleic anhydride) onto 5W25pts.wt. mixed rubber component consisting of 100W25pts.wt. ethylene-propylene rubber (e.g. an ethylene-propylene-diene terpolymer) and 0W75pts.wt. diene rubber (e.g. polybutadiene). Then 95W5pts.wt. component A and 5W95pts.wt. polyphenylene ether resin constituted of the repeating units of the formula [where n is 50W300; R1W4 each are a (substituted) hydrocarbon group, H, a halogen, cyano, a hydrocarboxyl, amino, etc.] are melt-compounded.