Objective To evaluate the molluscicidal activities of three Chinese plants N. indicum Mill, P. stenoptera DC, and R. japonicum Houtt, and to clarify the molluscicidal mechanism. Methods N-butanol extracts and water extracts of the three plants were obtained. The reactions of EST isozyme, glycogen and total protein of snails to the plant extracts were studied. Results EST electrophoresis showed that EST was an important antidotal enzyme system and reacted strongly to environment. EST changed greatly during the whole exposure period so that it could be viewed as a pathological index of toxicity. Extracts decreased the glycogen content of the snails’ soft tissues greatly, and also the protein content. Conclusion All extracts show strong molluscicidal activity. The LD50 value of the water extract of N. indicum Mill is as low as 13.2 mg/L. EST can be viewed as a pathological index of toxicity. The energy metabolism abnormity is the key reason for the molluscicidal activities. The biochemical mechanism needs further research. Objective To evaluate the molluscicidal activities of three Chinese plants N. indicum Mill, P. stenoptera DC, and R. japonicum Houtt, and to clarify the molluscicidal mechanism. Methods N-butanol extracts and water extracts of the three plants were obtained. EST lysozyme, glycogen and total protein of snails to the plant extracts were studied. EST electrophoresis showed that EST was an important antidotal enzyme system and reacted strongly to environment. EST changed changed during the whole exposure period so that it could be viewed as a LD50 value of the water extract of N. indicum Mill is as low as 13.2 Mg/L. EST can be viewed as a pathological index of toxicity. The energy metabolism abnormity is the key reason for the molluscicidal activities. The biochemi Cal mechanism needs further research.