To obtain a composition for crosslinking a chlorinated polyethylene, providing a rubber product made of a chlorinated polyethylene having inherent characteristics of an usual chlorinated polyethylene rubber and excellent water resistance.

This composition for a crosslinking chlorinated polyethylene comprises 100 pts.wt. of a chlorinated polyethylene, 0.5-20 pts.wt. of an acid acceptor, 0.5-7 pts.wt. of a crosslinking agent, 5-50 pts.wt. of white carbon and 0.5-10 pts.wt. of a polyhydric alcohol or its derivative. The preferable white carbon is silica by a dry method and/or silica by a wet method. The preferable polyhydric alcohol or its derivative is a glycol derivative, a glycerol derivative or a pentaerythritol derivative. The preferable crosslinking agent is an organic peroxide.