To provide a vinyl aromatic polymer composition comprising the vinyl aromatic polymer and a ketone polymer and having improved properties.

A vinyl aromatic polymer is a polymer for molding, preferably an acrylonitrile-butadiene-sytrene copolymer. A ketone polymer is the copolymer of carbon monoxide with one or more kinds of unsaturated compounds. The amount of the vinyl aromatic polymer is >50 wt.% to about 99.5 wt.% based on the total amount of the vinyl aromatic polymer and the ketone polymer, while the amount of the ketone polymer is about 0.5 wt.% to about <50 wt.%. Heat resistance and elongation are more improved than those in the case of the vinyl aromatic polymer alone.