Effects of maleimidophenylmethacrylates on thermal stability of polystyrene have been examined by dynamic thermogravimetric analysis in air conditions. The maleimidophenylmethacrylates with substitutes of various molecular architecture in imide cycle have been built in polystyrene macromolecular chains (as much as 1 mol %) by means of copolymerization reaction. The thermal stabilizing effects depend on the structure features of the used compounds. Some of the additives show the inhibiting effect only whereas other ones show combined inhibiting and retarding effects. The last ones revealed as very effective stabilizers of polystyrene against thermal oxidative degradation.