This paper has analyzed allelopathic effects ofNerium indicum on Oncomelania hupensis through triterpene sapogenins, a potential molluscicide. The snails were treated under six various concentrations （0, 20, 40, 60, 80, 100 mg/L） of triterpene sapogenins and five periods （1, 2, 3, 4, 5 days）. The mortality of snails was positively correlated with the concentration of triterpene sapogenins and exposure time. The results ofprobit analysis showed that the LD50 （Lethal Dose, 50%） oftriterpenoid saponins from N. indicum by immersion for 2, 3, 4, 5 days were 78.31, 30.26, 20.50, 14.19 mg/L, respectively. And the corresponding 95% confidence intervals were 63.60-108.19, 9.49-44.42, 2.86-30.90, 0.23-22.79 mg/L, respectively. The observations of both scanning electron microscope and transmission electron microscope proved that 40 mg/L triterpene sapogenins could cause apparent damage to the structure of soft tissue, liver and intestine of O. hupensis. The esterase （EST） isozyme electrophoresis in liver of O. hupensis treated by 40 mg/L of the concentrations lixivium of the triterpene sapogenins from N. indicum was analyzed for 24, 48, 72, 96, 120 h, respectively. The activity of enzyme was higher than control water group after been treated up to 24-48 h, and then lowered and disappeared after 72 h. It was implicated that the extracted triterpene sapogenin from N. indicum were promising for controlling the snail, which were also providing the foundation for constructing plant community of oleander to control O. hupensis.
