The liquefaction of low-density polyethylene was studied in several solvents with or without sulfur as an additive. With the addition of molecular sulfur in the liquefaction of polyethylene in 1-methylnaphthalene, the conversion increased from 77.8% to 100%, and the oil yield increased from 62.4% to 78.7% at 673 K, as compared to the conversion and yield results of the run in the absence of sulfur. The molecular weight distributions of the oil fraction, obtained in the presence of sulfur, shifted to the lower molecular weight side as compared to that obtained without sulfur. At an elevated temperature, molecular sulfur would generate sulfur radical, which abstracts hydrogen from polyethylene to initiate the chain reactions involved in the degradation of polyethylene. The promoting effect of sulfur on the degradation of polyethylene was affected by the chemical structure of the solvent. The promoting effect of sulfur was significant in aromatic and non-hydrogen donating compounds such as 1-metliylnaphtlialene, naphthalene, and toluene. However, in tetralin no promoting effect of sulfur was observed because the sulfur radical would abstract hydrogen from the solvent and polyethylene competitively.