The present invention provides a method for hydrogenating a metathesis polymer solution obtained by polymerization in the presence of a metathesis polymerization catalyst comprising (a) the catalyst component of a transition metal compound and (b) the co-catalyst component of a metal compound by bringing the above solution into contact with hydrogen, without adding an inactivating agent for the metathesis polymerization catalyst, that is, with the solution left to contain the catalyst, in the presence of a hydrogenation catalyst comprising a transition metal compound (c) and a reductive metal compound (d) and if necessary by adding an acid-binding compound. According to this method, both addition of the inactivating agent and removal of the metathesis polymerization catalyst are not necessary, and also the hydrogenation can be carried out at a lower temperature and under a lower pressure than in hydrogenation with a supported-type catalyst, so that the efficiency of production of the hydrogenated product is excellent. Besides, even if tungsten hexachloride (WCl.sub.6), etc. are used as the catalyst component, an effect of preventing a hydrogenation reactor from corrosion by a hydrogen halide, can be obtained.