A polyethylene for an insulation layer of a power cable, of which the dissipation factor never increases even in a high-temperature, high electric field, and a crosslinked polyethylene insulated power cable which uses this polyethylene so that the high-temperature dielectric breakdown voltage is large enough for high-capacitance transmission. This polyethylene is a low-density polyethylene which is synthesized by high-pressure radical polymerization of ethylene, and has properties including: a melt flow rate of 0.1 to 10 g/10 minutes; a density of 0.915 to 0.935 g/cm.sup.3 ; an absorbance of 0.03 to 1.0 for a ketone-type carbonyl group, having a peak in a position corresponding to a wave-number of 1,725.+-.4 cm.sup.-1 in an infrared absorption spectrum, an absorbance of 1.0 or less for an ester-type carbonyl group, having a peak in a position corresponding to a wave-number of 1,743.+-.4 cm.sup.-1 and absorbances of less than 0.03 for other carbonyl groups; and/or a content of 3% by weight or less for components eluted at a temperature not lower than an elution temperature T (.degree.C.) calculated as T=687.times.D-547, where D (g/cm.sup.3) is the density of the low-density polyethylene, in a CFC measurement.