PURPOSE: To obtain a polystyrene resin composition having high mechanical properties, etc., and improved flame-retardancy as well as antistaticity by adding a flame retardant such as organic halogen compound in combination with a specific antistatic agent to a polystyrene resin.

CONSTITUTION: The composition contains (A) a polystyrene resin, (B) a compound selected from an organic halogen compound and a phosphorus-containing compound (preferably an organic bromine compound such as decabromodiphenyl oxide, etc.) and (C) one kind of substance selected from among alkylene oxide adduct of saponified ethylene-saturated carboxylic acid vinyl ester copolymer, an inorganic alkali metal salt, an anionic surfactant, a cationic surfactant and a nonionic surfactant (preferably ethylene oxide adduct of saponified ethylene- vinyl acetate copolymer). The amounts of the components A, B and C are preferably 80-95wt.%, 1-20wt.% and 0.5-8wt.%, respectively.