PURPOSE: To obtain a resin composition which can give a molding that does not suffer from bleeding to the surface and generates neither corrosive nor noxious gases during processing or in burning and which is markedly improved in flame retardancy without detriment to the features of the thermoplastic resin.

CONSTITUTION: This resin composition is prepared by mixing 100 pts.wt. thermoplastic resin with 5-80 pts.wt. product of melt kneading of at least one acid- modified resin selected from among an acid-modified polystyrene, a graft compound thereof, an acid-modified acrylic resin and a graft compound thereof an at least one nonhalogenous flame-retarding compound selected from among a phenolic resin and phosphorus, nitrogen and boron compounds, and melt- kneading the resultant mixture.