Abstract: Objective To study the expressions of Fas and Fas-Ligand (FasL) genes in rats with acute pancreatitis (AP) and their relation to apoptosis of pancreatic acinar cells. Methods Rat models of acute pancreatitis with varied severity were established by retrograde injection of sodium taurocholate at different concentrations via the apancreatobiliary duct. The expressions of Fas and FasL mRNAs and proteins were detected by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. The apoptosis of acinar cells was quantified by in situ nick ending-labeling technique. Results of expressions fas, FasL mRNA and protein were colocalized in normal pancreatic acinar cells. Li pancreatic tissue with less severe inflammation, the expressions of Fas and FasL mRNA increased significantly, and the apoptosis index of the acinar cells was also elevated; with the increase in the severity of the pancreatitis, the expression of Fas and FasL mRNAs were gradually lowered and apoptosis index of the acinar cells was increased. Conclusion Fas/FasL system might be involved in the renewal and homeostasis of normal pancreatic tissue, and constitute an important pathway mediating the apoptosis of pancreatic acinar cells in AP .