PURPOSE: To obtain a thick-walled crosslinked polyolefin molded article having excellent flame retardance and uniformly crosslinked to the inner part, by compounding a metal hydroxide to a silyl-modified polyolefin and molding the composition at a temperature near the dehydration initiation temperature of said hydroxide.

CONSTITUTION: 100pts.(wt.) of a silyl-modified polyolefin is compounded with 1W80pts. of a metal hydroxide flame-retardant (e.g. aluminum hydroxide) and the obtained composition is extrusion-molded at a temperature near the dehydration initiation temperature of said metal hydroxide. The molded article can be crosslinked from the inner part of the article with water released from the metal hydroxide.