Abstract: To study the protective effect of Forsythia suspensa leaf extract (FSLE) on heat-stressed rats, thirty rats were randomly divided into control group, heat stress group, and FSLE low-dose group, FSLE medium-dose group, and FSLE high-dose group, artificial intelligent climatic chamber was uesd to establish the heat stress model of rats. At the end of the heat stress experiment, the growth performance, rectal temperature, organ index and other indicators of the rats in each group were analyzed. The pathological changes of the rats ileum and liver tissues were observed, and the contents of corticosterone (CORT) and adrenocorticotropic hormone (ACTH) in the serum were detected. The results showed that compared with the model group, the immune organ index of the FSLE high-dose group increased significantly(P<0.05). The levels of CORT and ACTH in serum were significantly reduced(P<0.05), and the injury of rats ileum and liver tissue was significantly improved. This study showed that FSLE had a certain protective effect on heat-stressed rats, and it could be used for the prevention of heat stroke.