The number of chitosan particles was observed to decrease throughout the reaction, and chitosan particles were undetectable in some instances. Thus, the ability of chitosans to inhibit hydrogen peroxide decomposition depended on the rate of metal-catalyzed hydrogen peroxide decomposition, the adsorption of metals onto chitosan and the consumption of hydrogen peroxide by the reaction between chitosan and hydrogen peroxide. When the consump- tion of hydrogen peroxide by the reaction between chitosan and hydrogen peroxide was more than the decomposition of hydrogen peroxide catalyzed by the metals, the residual hydrogen peroxide would decrease. The above-described results for pulp bleaching showed that both the brightness of the bleached pulp and the residual hydrogen peroxide decreased at a higher chitosan dosage, which was perhaps due to the increased hydrogen peroxide con- sumption by chitosan at high chitosan concentrations.