This study examined the mechanisms of molluscicide from Streptomyces violaceoruber. After snails were immersed in the liquid with Streptomyces violaceoruber or the de-chlorinous water or the culture medium for 36 hours，the Mg²⁺-ATPase, CHE, NOS, LDH and SDH in the liver, centric ganglions, head-foot muscles and ctenidia of Oncomelania hupensis were characterized by enzyme-histochemistry technology and changes of them were observed closely. Results show that the activity of Mg²⁺-ATPase in the liver, centric ganglions, head-foot muscles and ctenidia decreased noticably or disappeared after snails were immersed in the liquid with Streptomyces violaceoruber for 36 hours. The activity of LDH in centric ganglions, head-foot muscles of the snail decreased in some degree. There isn’t much difference between the de-chlorinous water group and the liquid with Streptomyces violaceoruber group in the activities of NOS, CHE and SDH. The activities of Mg²⁺-ATPase, CHE, NOS, LDH and SDH at counterparts of the snail’s respectively grown in de-chlorinated water and in the culture medium were identical. The results indicate the mechanism of molluscicide coming from Streptomyces violaceoruber is that the Mg²⁺-ATPase and LDH are destroyed, and formation and release of ATP in the liver, centric ganglions, head-foot muscles and ctenidia are stopped. Cessation of vital functions casues deathof snails [Acta Zoologica Sinica 52(1): 109–114,2006].