PURPOSE: To improve physical-mechanical, tensile and thermal properties by incorporating a polyphenylene ether and a specific high-impact vinyl aromatic polymer.

CONSTITUTION: A composition is obtained by mixing (A) 5-60 wt.% polyphenylene ether having an average molecular weight of 5,000-120,000, and (B) 95-40 wt.% high-impact vinyl aromatic polymer containing (I) 30-90 wt.% polymodal vinyl aromatic monomer-conjugated diene block polymer having 55-85 wt.% vinyl aromatic monomer and represented by formula I or II (wherein S1 and S2 are each a non-elastomeric polymer block of a vinyl aromatic monomer; B, B1 and B2 are each an elastomeric copolymer block based on a conjugated diene) and (ii) 70-10 wt.% vinyl aromatic polymer containing 5-15 wt.% dispersed dienic rubber in the form of particles having a cellular structure and an average chord of not less than 1.2 Mm, wile, if necessary, adding not more than 50 wt.% reinforcing material such as an inorganic fiber, 0.05-5 wt.% stabilizer and an additive, optionally, at a temperature of 200-300°C.