Novel carboxyalkyl chitosan derivatives were prepared by reacting chitosan with 4-chlorobutyric acid or 5-chlorovaleric acid. The carboxyalkylation process was affected by the reaction medium, the reaction temperature, and the presence of catalytic base. The highest degree of substitution for chitosan derivatives was obtained from the reaction at 50℃ in methanol medium without base. Prepared carboxyalkyl chitosan derivatives exhibited the decreased crystallinity, which was confirmed by X-ray diffraction and thermogravimetric analysis. As a consequence, the carboxyalkyl chitosan derivatives showed an improved solubility in various solvents. Antibacterial activities of chitosan and carboxyalkyl chitosan derivatives against E.coli (ATCC 14339) and S. aureus (ATCC 6538P) were investigated by the viable cell counting method, and the carboxyalkyl chitosan derivatives showed higher antibacterial activity than chitosan. They also exhibited the high activity against E. coli, which is comparable to the activity S. aureus.