To provide a method for processing to modify an artificial cellulose- based fiber capable of effectively imparting color development in super dark colors and high stress resistance and, further, excellent water retention and absorption and soft hand feeling without reducing wet fastness to an artificial cellulose fiber or a fabric containing the same fiber.

(1) This method for modifying an artificial cellulose-based fiber is to apply a glyoxal-based resin, an acid catalyst or a latent acid catalyst and a third ingredient which is at least one species selected from propylene glycol or its polymers, aliphatic polyols, reducing sugars, disaccharides and monosaccharides and subsequently heat treating the fiber. (2) The method for modifying the artificial cellulose-based fiber is to rub the fabric in a liquid flow after the aforesaid heat treatment.