PURPOSE: To prepare the titled crosslinked resin having high gel fraction and excellent heat resistance, by grafting a specific ethylenic unsaturated silane compound in the presence of an antioxidant to a propylene resin, thereby preventing the deterioration of the base resin during grafting.

CONSTITUTION: 100pts.wt. of a propylene resin[e.g. a copolymer (mixture) with 0W30wt% other α-olefin]is mixed with preferably 0.1W10pes. of an ethylenic unsaturated silane compound of formula[R is ethylenic unsaturated hydrocarbon(oxy); R' is saturated aliphatic hydrocarbon; Y is hydrolyzable organic group; n is 0, 1 or 2](e.g. vinyltrimethylsilane), 0.01W2pts. of a radical generator (e.g. benzoyl peroxide) and 0.01W5pts. of an antioxidant (e.g. 2,6-di-t-butyl- 4-methylphenol), and made to react at or above the decomposition temperature of the radical generator using, e.g. an extruder.