PURPOSE: To provide the titled composition significantly improved in rigidity without impairing appearance and impact strength, for use in molding thermoplastic synthetic resin molded articles, comprising a rubber-reinforced polystyrene resin, fibrous potassium titanate and higher fatty acid (metal salt) in specified proportion.

CONSTITUTION: The object composition comprising (A) 100pts.wt. of a rubber- reinforced polystyrene resin (e.g. prepared by dissolving a rubbery substance such as polybutadiene in an aromatic monovinyl monomer such as styrene followed by e.g. bulk polymerization), (B) 2W50pts.wt. of fibrous potassium titanate (pref. with an average fiber length of 10W30μ and fiber diameter of 0.1W0.8μ), and (C) 0.1W5pts.wt. of a higher fatty acid (metal salt) [e.g., stearic acid (or zinc stearate)].