PURPOSE: The titled composition that is obtained by adding hydrotalcite or the like to a composition which contains polyethylene and halogen-containing flame retarder and crosslinking with an organic peroxide, thus showing excellent electric insulation, heat resistance and flame retardancy.

CONSTITUTION: In the composition which is composed of 100pts.wt. of polyethylene or a copolymer mainly consisting thereof and 5W10pts.wt. of a halogen-containing flame retarder such as decabromodiphenyl ether and is to be crosslinked with an organic peroxide, preferably dicumyl peroxide, 2W200pts.wt. per 100pts. wt. of the halogen-containing flame retarder, of hydrotalcite of the formula (x is 4W6; y is 1W3; z is 10W18; w is 0W4) and preferably an antioxidant such as dilauryl thiodipropionate are added. The composition is obtained by mixing all of the constituents except the organic peroxide on the test roll, then admixing the peroxide and kneading them.