Cotton fibers were pretreated with NaOH, $NH_3$, NaOH/$NH_3$ and subsequently they were processed with an enzyme(cellulase). Weight loss and dyeing properties were investigated in relation to fine structure of the fiber. The crystal lattice of cellulose I was transformed into cellulose II and cellulose III by NaOH and $NH_3$ treatments. In the case of NaOH treatment, transforming to cellulose II was not readily observed higher temperature. The moisture regain was Increased by NaOH and $NH_3$ treatment and reduced by NaOH treatment at 80 $^{circ}C$. Weight loss of the pretreated-fibers with NaOH was greater at 20 $^{circ}C$ than at 50 $^{circ}C$ and 80 $^{circ}C$, while that of $NH_3$ or NaOH/$NH_3$ pretreated-fibers was smaller than that of the NaOH-treated fiber. Equilibrium dye exhaustion was greatly increased from the untreated fiber by NaOH treatment, while slightly increased by $NH_3$ or NaOH/$NH_3$ treatment. Equilibrium dye exhaustions of the pretreated cotton fibers were decreased with an increase of the time of cellulase treatment. It was explained as amorphous region for dye adsorption was decreased by enzymatic weight loss. It is obviously explained that equilibrium dye exhaustion of the NaOH, $NH_3$ and cellulase-treated fibers well agreed with the tendency of the amount of weight loss.