Depolymerization of the biopolymer chitosan by an autoclaving process at 121degreesC and 15 psi was investigated using various treatments. Acetic acid was found to be the most effective solvent in decreasing chitosan viscosity among the six organic acids tested. The rate of viscosity decrease increased with increasing chitosan concentration. The viscosity of 1% chitosan in 1% acetic acid decreased rapidly to 91% of the initial viscosity following the initial 15 min of autoclaving. This decreased gradually to 93% and 94% in 30 and 60 min, respectively, without being adversely affected by the chitosan solution volume. The degree of deacetylation was comparable before and after autoclaving for 60 min. Chitosan at three molecular weights (M-r = 1597, 1110, and 789 kDa) decreased in molecular weight by 46%-51% in the 15-min treatment, 55%-60% in the 30-min treatment, and 60%-62% in the 60-min treatment. The addition of 0.1%-1.0% (v/v) concentrations of hydrogen peroxide to the chitosan solution autoclaved for 15 min decreased viscosity by 94%-98% and molecular weight by 69%-83%. This process is a simple, timesaving, homogeneous depolymerization procedure, and it is possible to prepare partially hydrolyzed chitosan with specified molecular weights by regulating the time of treatment. (C) 2003 Wiley Periodicals, Inc.