The chitosan was degraded by the cheap, efficient, and commercially available enzymes in hydrochloric acid solution. The effect of molar ratio of added HCl to -NH2 of chitosan on the degradation was investigated, and the favorable ratio was between 0.50 and 0.95. The chitooligomer hydrochlorides were directly prepared by this simple method. The chitooligomer hydrochlorides were characterized by thermogravimetric analysis, differential thermal analysis, and Fourier transform infrared. These results show that the obtained chitooligomer hydrochlorides were much more stable than the chitooligorner acetates. This preparation procedure of chitooligomer hydrochlorides was simple and cheap, and helpful for the preservation of chitooligomers. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114:956-961, 2009