Abstract: There is disclosed a process for preparing impact resistant styrene graft copolymers having improved properties, especially a high gloss. They are obtained by polymerizing a solution of an ethylene/propylentercomponent rubber in a mixture of styrene and acrylonitrile in one step (mass polymerization) or two steps (mass/suspension polymerization) in the presence of an organic peroxide and submitting the polymer to a two step extrusion, the first step being carried out at temperatures of from 130.degree. to 240.degree. C, the second step at temperatures of from 200.degree. to 280.degree. C, and providing that during the second extrusion step a quantity of about 0.05 to about 0.5% by weight of the organic peroxide is still present.