PURPOSE: To obtain a polystyrene blend having high heat resistance and holding high impact properties by adding a high impact polystyrene, a specific vinyl aromatic copolymer and a styrene graft rubber concentrate.

CONSTITUTION: A polymer blend is obtained from a high impact polystyrene (A) (e.g. one derived from a butadiene/styrene block copolymer and styrene, etc.), a copolymer (B) obtained by anionically polymerizing a vinyl aromatic monomer (e.g. styrene, etc.), produced at a temp. higher than the ceiling temp. of α-methylstyrene and a styrene grafted rubber concentrate (e.g. styrene grafted butadiene homopolymer, etc.), (C). In this blend, high heat-resistance incapable of being usually obtained in an impact polystyrene polymer is obtained and high impact properties capable of usually resulting in high impact (rubber modified) polystyrene is held.