To improve wet color fastness in washing, etc., of a cellulose fiber material, such as a jean product and a denim raw fabric, which is dyed with an indigo dye or a sulfur dye.

A method for treating the cellulose fiber material is used for improving the wet color fastness in washing, etc., of the cellulose fiber material which is dyed with the indigo dye or the sulfur dye, wherein the cellulose fiber material is treated with an aqueous solution containing a cationic polymer compound which is composed of structural units derived from diallyamine in the presence of an alkali agent.