The performance of montmorillonite and pyrophyllite clays in the degradation of polystyrene (PS) was investigated in this study. The catalytic degradation was carried out in a semi-batch reactor with a mixture of polystyrene and catalysts at 400-450 ℃. The catalysts showed good catalytic activity for the degradation of PS. Styrene is the major product, and ethylbenzene is the second most abundant one in the liquid product. The catalytic degradation showed much less production of styrene dimmers and higher selectivity to ethylbenzene than the thermal degradation did. High degradation temperature favored the production of styrene monomer. but it decreased the ethylbenzene production.