The γ-radiation-induced cross-linking of polyethylene was studied in vacuo at 30—200°C with a dose rate of 1.1×105 rad/hr. The gel fraction increased with rising irradiation temperature, and become almost constant above 150°C. The degree of increase was extremely large at near the melting temperature of polyethylene. The dosage to produce gelation decreased with the temperature, but was almost constant above 150°C. The gel fraction was increased by irradiation beyond the gel-point dosage at each temperature, and the relative increment decreased with the radiation dose. The amount of hydrogen formation was found to increase to some extent with temperature. The content of trans-vinylene unsaturation increased almost linearly with the dose, and the extent of the increment was little affected by the temperature. At 150 and 200°C, the methyl-group content also increased almost linearly with the dose, and the rate of increase was somewhat higher at 200°C than at 150°C. On the basis of these results, the mechanism of the γ-radiation-induced cross-linking of polyethylene was discussed.