Objective To investigate the protective effect of castanospermine (CS) on renal injury induced by severe acute pancreatitis (SAP) in rats and its possible mechanism. Methods Twenty-four SPF adult male Sprague Dawley rats were randomly divided into three groups: shame operation group (SO group, n=8), SAP group (n=8), and CS group (n=8). SAP models were induced by retrograde injection of 5% sodium taurocholate (1 mL/kg) in biliopancreatic duct in the SAP group and the CS group. CS solution (200 mg/kg) was immediately administered via intraperitoneal injection after the induction of pancreatitis in the CS group. Rats in the SO group were subjected to a sham surgery that the pancreas and duodenum were flipped a number of times. All rats were sacrificed at 12 h after modeling. Blood samples were collected by inferior vena cava puncture, and serum activities of amylase (AMY), levels of blood urea nitrogen (BUN) and creatinine (Cr) were measured by using a fully automatic chemistry analyzer. The head of pancreas and renal tissues were harvested and pathological change was observed under the light microscope. Expressions of nuclear factor-κB (NF-κB), tumor necrosis factor-α (TNF-α), intercellular adhesion molecule-1 (ICAM-1), and Caspase-3 in renal tissues were evaluated by immunohistochemistry assay. Results ① Compared with the SO group, the damages of the pancreas and kidney tissues were significantly worse in the SAP group, and the above damages in the CS group were significantly decreased when comparing with the SAP group. ② Compared with the SO group, the serum activities of AMY, levels of BUN and Cr were significantly increased in the SAP group (P<0.05). The serum activities of AMY, levels of BUN and Cr in the CS group were significantly lower than those of the SAP group (P<0.05). ③ Compared with the SO group, the integrated optical density (IOD) of NF-κB, TNF-α, ICAM-1, and Caspase-3 in renal tissues were significantly increased in the SAP group (P<0.05), and the above indicators in kidney tissues of the CS group were significantly decreased when comparing with the SAP group (P<0.05). Conclusions CS can mitigate severe acute pancreatitis-induced renal injuries in rats, it ameliorates renal injury and improves renal function. The mechanism for the above improvements is that CS can widely inhibit the activation of NF-κB, and then downregulate the expressions of TNF-α, ICAM-1, and Caspase-3.