Characteristical patterns of non-specific esterase zymogram on the keratinization were carried out in the experimentally induced epidermoid carcinoma from the skin and salivary gland of mice. Zymogramic findings and histochemical localizations of esterase in tumor lesions were also comparatively observed. 1. Esterase zymogram of well keratinized carcinoma was characterized by intense stainability of the A-esterase and by relative decrease of the B- and C-esterases, although that in the homologous skin and salivary gland consisted of the A-, B- and C-esterases. 2. In zymogramic findings of esterase, the A-esterase was discriminated into the A-I and the A-II esterase. The A-I and A-II esterases were suggestive to be arylesterase and pseudocholinesterase from inhibitory attitude respectively. 3. Histochemical localization of esterase in well keratinized tumor tissues was not similar in the substrates used, that is, simple naphthol method stained in peripheral tumor cells, however substituted naphthol method showed an intense stainability in keratinized arears.