Study of the content of composite polystyrenefullerene samples prepared from solution by the solvent evaporation method have been performed with the size exclusion chromatography, translation diffusion, viscometry and electrooptical Kerr effect techniques. It was established that polystyrene interacts with fullerene C 60 in benzene without any special treatment at room temperature just after the mixing of polymer and fullerene solutions. The product of this interaction contains initial polystyrene and low molecular fullerene adducts that appear as a result of depolymerization of a significant part (up to 40 wt.%) of polymer chains.