The studies on the pyrolysis of polyethylene (PE), polypropylene (PP), and waste PE, PP with the continuous pyrolysis apparatus equipped with the 90 and 20mm pitch twin screw were carried out.There plastics were pyrolyzed to the hydrocarbon mixtures with a wide range of carbon number, under the reaction Condition which temperature and the feed rate of materials and the rotation rate of twin screw were 500-600°C, 1-5kg/hr, and 3-30rpm, respectively.The pyrolysis of PE, PP and these wastes were resembled each other in respect of the pyrolysis products. In any case, the component and the yield of product were greatly influenced by the temperature, but the rotation rate of twin screw and the feed rate of material did not have a pronounced effect on the yield of low molecular weight products.The gaseous products were obtained in 10-80wt% yields, which increases with greatly increasing the temperature, and they were contained 60-80 wt% olefins, and had high calorific value from 15, 000 to 20, 000 kcal/Nm3.The fractions distlling under 200°C were obtained in 10-40wt% yields. The contents of olefins, aromatics and paraffins in these fractions were 50-90wt%, 2-40wt%, and 5-30wt%, respectively. The contents of paraffins in the fractions decrased appro-ximately in propotion to increase in the temperature. In most cases, these fractions contained a large quantity of olefins and not fitted to fuel.The residue distilling at above 200°C were composed of hevay oils and waxes, having 200-350 of mean number molecular weight.