Objective To study the carcinogenesis of Simotang Oral Liquid in SD rats.Methods Totally 600 SD rats were randomly divided into five groups, half male and half female in each group.They were neg. control group, adjuvant control group, low, middle and high dose group, Sterilized water for injection, adjuvant solution, 1, 5, 25 g/kg Simotang oral liquid were ig given resp., Once a day for 104 wk.The clin. observation, body weight, food intake, gross anatomy and histopathol. of animals were examined during the experimentCalculation of mortality and tumor incidence in rats.Results There was no significant difference in survival rate among the exptl. groups.No regular change of toxicol. significance was found in the tumors of each exptl. group.Histopathol. examination showed that there was no significant dose-dependent relationship between tumor occurrence in each dose group, the occurrence of tumor is also a common predictable or sporadic tumor in the 2-yr carcinogenesis test of SD rats, the occurrence of these tumors is not related to the given test article.There was no increase in the incidence of test article related non-tumor lesions in all drug groups.Conclusion Simotang oral liquid was not found carcinogenicity in SD rats.