To explore the killing mechanism of META-Li against Oncomelania hupensis by observing the change of enzyme activity in snail tissue.Sixty snails were divided into 2 groups. Snails in experiment group were immersed in META-Li (100 mg/L) for 2d and soft tissue was separated for frozen sections. Histochemical staining for the enzymes CCO, LDH, SDH, AChE and NOS was done by routine method and the average grey density was measured under microscopy. Tissue sections of 10 snails were used to detect grey density for each enzyme. Snails without META-Li treatment served as control.The enzyme activity of CCO and AChE in the experiment group was significantly lower than that in the control (t=12.26, P0.05).The snail-killing effect of META-Li may be relevant to the enzyme activity in energy metabolism and the blocking of the nerve transmission.