We have investigated the catalytic degradation of polystyrene(PS) in a pyrex reactor. We have used silica-alumina and zeolites(ZSM-5, SCLZ, natural zeolite, etc) as acidic catalysts. They have been ion-exchanged with hydrogen form. The products of PS degradation were analyzed by gas-chromatography(GC-MS) and distributed in a narrow range of carbon number comparing with those obtained by thermal degradation. The liquid fraction of PS degradation consisted of aromatics. The catalytic degradation of PS was dependent on active sites of catalyst pellets rather than pore size and acid density of catalysts.