Pyrolysis of high density polyethylene(HDPE) was carried out to find the effects of temperature and time on the pyrolysis. The starting temperature and activation energy of HDPE pyrolysis increased with increasing heating rate. In general, conversion and liquid yield continuously increased with pyrolysis temperature and pyrolysis time. This tendency is very sensitive with pyrolysis time, especially at 45$0^{circ}C$. Pyrolysis temperature has more influence on the conversion than pyrolysis time. Each liquid product formed during pyrolysis was classified into gasoline, kerosene, light oil and wax according to the distillation temperature based on the petroleum product quality standard of Korea Petroleum Quality Inspection Institute. As a result, the amount of liquid products produced during HDPE pyrolysis at 45$0^{circ}C$ was in the order of light oil > wax > kerosene > gasoline, and at 475$^{circ}C$ and 50$0^{circ}C$, it was wax > light > oil > kerosene > gasoline.