Hydrolysis reactions using two kinds of water-soluble chitin derivatives and egg white lysozyme were carried out. The optimum pHs of the lysozyme were 5.0 and 3.8 for CM- and DHP-chitin, respectively. There were large differences in the reactivities, that is, in the case of DHP-chitin the reactivity was 7.9-10% of that for CM-chitin.