Objective To explore the effects of ulinastatin (UTI) on renal apoptosis and expression of bcl-2 in rats with severe acute pancreatitis (SAP). Methods Sixty rats weighing 250-300 g were randomized divided into 3 groups: pseudo-operation group (SO group, n=20), SAP group (n=20) and UTI treated group (UTI group, n=20). The model of SAP was established by retrograde injection of 5% sodium taurocholate solution into the biliopancreatic duct in the rats. Serum Cr and BUN were determined. The left kidneys were resected for light and electronic microscopic study. Renal cell apoptosis was determined by TUNEL. Expression of bcl-2 was detected by immunohistochemical staining of SABC. Results Serum Cr, BUN, renal cell apoptotic index and bcl-2 expression were markedly increased in SAP group compared with SO group （P＜0.05， P＜0.01）, Renal tissue injuries were aggravated in SAP group under light and electronic microscopic study as well. In UTI group, serum Cr, BUN and renal cell apoptotic index were decreased significantly while the expression of bcl-2 increased remarkably and renal tissue injuries relieved compared with SAP group （P＜0.05）. Positive correlations were found between the renal cell apoptotic index and BUN as well as Cr (r=0.807, P＜0.05; r=0.812, P＜0.05). Conclusion The protective effect of UTI on SAP renal injury is probably through increasing bcl-2 expression and decreasing apoptosis.