To obtain the subject catalyst liquid capable of reducing an offensive smell of a formed material and an amount of a smoke generated at a formation thereof, and improving a heat resistance.

This metathesis polymerization catalyst is obtained by affecting an ether compound (e.g.; ethylene glycol dimethylether) with WCl6, MoCl5 WOCl4 and/or MoOCl3 and also without affecting a phenolic substance. The catalyst liquid contains a compound of the formula [(x) is 0-3; OR is an alkoxy, R is a (substituted) alkyl; L is a chain like ether compound; (s) is 1-3]. The catalytic liquid is used for a method for obtaining a crosslinked polymer composition formed by mixing (A) a monomer liquid consisting of a metathesis polymerizable cyclic olefin (e.g.; cyclopentadiene) containing a catalyst component (a catalyst liquid) of a metathesis polymerization catalyst with (B) an activating agent component for the metathesis polymerization catalyst system (e.g.; chlorodiethyl aluminum), pouring the mixture liquid into a mold, performing a polymerization and a crosslinking in the mold.