Abstract: Objective To study on the mechanisms of natural compounds extracted from alternanthera philoxeroides killing snails.Methods Snails were immersed in aqueous extractant of alternanthera philoxeroides(1g/100ml)or dechlorinated water for 24h,and then the ultrastructures of the liver and intestine from the snails were observed by using a transmission electron microscopy (TEM).Results After snails were immersed in aqueous extractant of alternanthera philox eroides for 24h,hepatocytes of the snails were destroyed noticeably and pericellular membrane was erosion.The numerous vesicles and vacuoles were formed in cytoplasm.Mitochondria and rough endoplasmic reticulum were markedly vesiculated.Secretory granules in cytoplasm were pycnosis,while the number of secondary lysosomes and autophagosome were increased.Nuclei were karyopyknosis and karyothecas were fragmentary.Nuclei of intestinal epithelial cells were a slight swelling,and their gap between intestinal epithelial cells became clearly enlarged,and there were clear region in and between intestinal epithelial cells.Conclusion Aqueous extractant of alternanthera philoxeroides can harm hepatocyte and cause edema in and between intestinal epithelial cells of oncomelania hupensis.