The chlorination and oxidation activity of chloroperoxidase (CPO) was enhanced 32 and 20% by chitosan, and oxidation activity 24% by thioglycolic acid, respectively. The pH optimum of chlorination reaction shifted 3 units to a less acidic environment by chitosan (from 2.75 to 5.75). The kinetic parameters indicated both the affinity and specificity of CPO to substrate were improved.