Gynostemma pentaphyllum (Thunb) Makino is a kind of natural plant growing in the southern provinces of China. In this experiment, rats were given drinks of 2% Gynostemma Pentaphyllum (Thunb) makino aqua boiled solution freely for 2 weeks before administration of carcinogen. Subsequently, the rats were injected with carcinogen (MANA) for 18 weeks and were sacrificed at intervals. The result showed that the number of cases of esophageal epithelial papilloma, the average number of tumor and the incidence of esophageal cancer in the experimental group were lower than those in the control group (MANA only), though no statistical significant difference was found. The initiation of cancer was delayed for 6 weeks. These indicated that Gynostemma Pentaphllum Makino might have some preventive and blocking effect on esophageal cancer in rats.