Cotton fabric was treated with chitosan solution to impart antimicrobial property. Effect of treatment conditions and degree of deacetylation of chitosan(DAC) on the antimicrobial property and the durability to laundering were examined. Five types of chitosan were used; similar molecular weight and different DAC as 65, 78, 84, 95, and 99 percent, respectively. Cotton fabric was impregnated with 0.1~1.0% chitosan solution at $25^{circ}C$, pre-dried, and cured at 15$0^{circ}C$ for 3 min or not cured. Antimicrobial activity was evaluated by the Shake Flask Method using Staphylococcus aureus. The durability to washing of finishing effect was examined by washing up to 20 times. Bacteria reduction rates of treated samples increased as the concentration of chitosan solution increased. The antimicrobial effect of chitosan increased with the increase of DAC; i.e., the increase of the number of amine group. The cured samples showed better durability to washing comparing with not-cured samples, and the curing effect on the durability to washing in-creased markedly as the concentration of chitosan solution increased.