Objective To explore the protective effect of rapamycin on brain tissues injury in severe acute pancreatitis (SAP) and its possible mechanism in experimental rats. Methods Ninety SPF males SD rats were randomly divided into 3 groups by random envelope opening method: sham operation group (SO group), SAP group, and rapamycin group (RAPA group), then the rats of each group were divided into 24 h, 36 h, and 48 h 3 subgroups by random number table method. Rats in each group underwent laparotomy, the model was prepared by retrograde injection of solutions into biliopancreatic duct, rat of the SO group was injected with 0.9% normal saline (2 mL/kg), rats of the SAP group and the RAPA group were injected with 5% sodium taurocholate solution (2 mL/kg), but rat of the RAPA group was injected with rapamycin (1 mg/kg) at 30 min before narcosis. All survival rats in each subgroup were killed at 24 h, 36 h, and 48 h respectively, then the pancreas and brain tissues of rats were collected, pancreas and brain tissues were stained by hematoxylin-eosin staining, brain tissues were stained by Luxol fast blue additionally, pathological changes of brain tissues were scored under light microscope. The protective effect of rapamycin on brain tissues injury was determined by comparing the differences in the degree of brain tissues among 3 groups. The phosphorylated mammaliantarget of rapamycin (p-mTOR) and phosphorylated ribosomal 40S small subunitS6 protein kinase (p-S6K1) expression levels in brain tissues were detected by Western blot. In addition, the correlations between the expression levels of p-mTOR and p-S6K1 in brain tissues and the degree of brain tissues injury were analyzed to further explore the possible mechanism of rapamycin’s protective effect on brain tissues injury in SAP. Results① At the point of 24 h, 36 h, and 48 h, the order of the relative expression levels of p-mTOR and p-S6K1 in brain tissues of three groups were all as follows: the SO group < the RAPA group < the SAP group (P<0.05). ② At the point of 24 h, 36 h, and 48 h, the order of brain histological score in three groups were all as follows: the SO group < the RAPA group < the SAP group (P<0.05). ③ The relative expression levels of p-mTOR and p-S6K1 in brain tissues were positively correlated with pathological scores of brain tissues (r=0.99, P<0.01; r=0.97, P<0.01). ConclusionRapamycin plays a protective role in pancreatic brain tissues injure by down-regulating the expression levels of p-mTOR and p-S6K1 in mTOR signaling pathway.