Objective To investigate the effect of pirfenidone (PFD) on pancreatic injury in rats with acute pancreatitis (AP) and its mechanism of action.Methods Thirty-two SPF male SD rats were randomly divided into control group, AP group and low- and high-dose PFD groups, with 8 rats in each group. AP models were successfully established in the AP group, and low- and high-dose PFD groups. Rats in the low- and high-dose groups were intragastrically administrated with PFD at doses of 50 mg/(kg·d) and 150 mg/(kg·d) for 24 hours, respectively, while those in the AP group and the control group were given the same amount of 0.5% sodium carboxymethyl cellulose. After the intervention, the volume of ascites and serum levels of amylase (AMY) and inflammatory factors were measured, and the histopathological changes of the pancreatic tissues were observed and scored in each group. Besides, the expressions of proteins associated with the Toll-like receptor 4/myeloid differentiation 88 (TLR4/MYD88) pathway in the pancreatic tissues of rats in each group were also compared.Results The volume of ascites, serum levels of AMY, IL-6 and TNF-α, the histopathological scores of the pancreatic tissues, and the protein expressions of TLR4 and MYD88 in the AP group were higher than those in the control group (P < 0.05), while they were lower in the low- and high-dose PFD groups than those in the AP group (P < 0.05) and were even lower in the high-dose PFD group than those in the low-dose PFD group (P < 0.05).Conclusions PFD has a protective effect on pancreatic injury in rats with AP, and its mechanism may be related to the inhibition of TLR4/MYD88 signaling pathway activation.