Converting of wasted plastics into oil can be used as an energy source. It has advantages of reducing the environmental problems and produces additional economic values. In this study, polyethylene and polypropylene were catalytically degraded by JSA-1 (Si/Al=6.7), JSA-2(Si/Al=2.57) and HZSM-5 (Si/Al=30.2) catalysts to investigate the optimum conditions. The order in liquid product yield was JSA-2 > JSA-1 > HZSM-5. Liquid product yield was increased with the catalyst loading, but the carbon number distribution of the liquid product was widely spreaded. When the HZSM-5 was phosphated to regulate the acidic amount and strength, the liquid product yield was in the order to P (2 wt%) HZSM-5 > P (1 wt%) HZSM-5 > HZSM-5 > P (3 wt%) HZSM-5. The optimum acidic amount and strength of the phosphated HZSM-5 was achieved when 2 wt% P was loaded. It was confirmed by the ammonia TPD.