To produce a cobalt soap desirable in transportation, handling properties, and forming and processing properties, and having the high softening point by bringing an oxidative gas or an oxidizer into contact with the cobalt soap having a C=C bond in the molecule.

An oxidative gas (e.g. oxygen, ozone, nitrogen oxide or the like) is brought into contact with a cobatt soap having a C=C bond in the molecule, preferably while heating the cobalt soap to the temperature from the softening point of the soap to 200°C and preheating the gas when the gas is blown in so as not to reduce the heated temperature of the soap to provide the objective cobalt soap (e.g. cobalt naphthenate) having a raised softening point. In the other method, the cobalt soap is dissolved in an organic solvent such as xylene, and an aqueous solution containing an oxidizer (e.g. hydrogen peroxide and a solution containing nitric acid) is added thereto and vigorously stirred also to provide the objective cobalt soap.