Water-soluble chitosan with low molecular weight was prepared by the depolymerization of chitosan with aqueous H2O2 solution. The IR and H-1-NMR studies verify that depolymerization leads to the breakage of 1,4-beta-D-glucoside bonds of chitosan. X-ray analysis shows the depolymerization takes place at the surface of the chitosan in crystal region by so called peeling-off process while the amorphous portion is depolymerized by penetrating pattern. (C) 2003 Kluwer Academic Publishers.