PURPOSE: To improve the color yield and wet fastness of a cellulose fiber dyed with an anionic dye by treating the fiber with a specific quaternary ammonium salt before or during the dyeing treatment.

CONSTITUTION: Before or during the dyeing of a cellulose fiber with an anionic dye such as a direct dye, a quaternary ammonium salt of formula I (R is a 1-3C alkyl, especially methyl or ethyl; X is a group of formula II or formula III; Hal is a halogen; Q- of formula IV is an anion of an aromatic sulfonic acid or a 1-3C alkyl sulfate ion) is fixed to the cellulose fiber preferably by cold pat batch process (treatment for 4-48 hr at room temperature). The quaternary ammonium salt is preferably N-epoxy-2,3-propyl-N-methyl-N,N- diallylammonium methyl sulfate, N-(3-chloro-2-hydroxypropyl)-N-methyl-N,N- diallylammonium methyl sulfate, etc.