Objective To investigate the changes of expression of zonula occludens-1(ZO-1) in rats with severe acute pancreatitis (SAP), and to study the relationship between the ZO-1 protein and microvascular injury in rats with SAP. Methods Forty-eight Wistar rats were randomly divided into sham-operation (SO) group and SAP group, each group enrolled 24 rats. Pancreas of rats in SO group were flipped only after laparotomies, but rats of SAP group were injected with 5% sodium taurocholate by retrograding cholangiopancreatography micro pump to produce the SAP model. At 6, 12, and 24 hours after operation, 8 rats were sacrificed to get abdominal aortic blood for testing the levels of peripheral blood amylase, trypsin, interleukin-8(IL-8), tumor necrosis factor-α(TNF-α), and ZO-1 protein. At the same time, pancreatic tissues were got to perform HE staining and immunohistochemical staining for observation of the pathological changes and the expression of ZO-1 protein respectively. Results Compared with SO group at the same time, the levels of peripheral blood amylase, trypsin, IL-8, TNF-α, and ZO-1 protein were all higher in SAP group (P < 0.05). The level of amylase in SAP-24 hours group was higher than those of 6 hours group and 12 hours group(P < 0.05), the levels of trypsin, IL-8, and ZO-1 protein in SAP group increased over time (P < 0.05), but levels of TNF-αin 3 time points of SAP group did not differ with each other significantly(P > 0.05). Results of regression showed that in the SAP group, the level of ZO-1 protein in serum was significantly positive correlated with pathological score of pancreatic tissue(b=0.96, P < 0.05), levels of serum amylase(b=0.87, P < 0.05), trypsin(b=0.72, P < 0.05), and serum IL-8 (b=0.69, P < 0.05), but was not significantly correlated with level of TNF-α(P > 0.05). HE staining results showed that damage of pancreatic tissues became worse over time in SAP group, and the pathological score of SAP-6 hours group was lower than those of 12 hours group and 24 hours group (P < 0.05). Immunohistochemical staining results showed that, in SAP group, with the extension of time, the number of ZO-1 protein granules in pancreatic acinar cells and capillary wall reduced, and expressed in capillaries discontinuously. Conclusion During the course of SAP, the concentration of serum ZO-1 protein increase, but its expression in the pancreatic tissue degrade, which is closely associated with microvascular injury and progression of pancreatic tissues.