Objective:To evaluate the effect of ulinastatin on the postoperative pulmonary complications (PPCs) in the patients undergoing off-pump coronary artery bypass grafting (OPCABG).Methods:Medical records from patients scheduled for elective OPCABG from September 2021 to August 2023 were retrospectively collected. The patients were divided into ulinastatin and control groups based on the intraoperative use of ulinastatin. Confounding factors were adjusted using propensity score matching and an extended Cox proportional hazards model. The primary outcome was the development of PPCs within 30 days after surgery, and secondary outcomes included length of stay in intensive care unit, length of hospital stay and occurrence of other adverse events.Results:A total of 1 532 patients were included in this cohort study, and 585 cases (38.2%) experienced PPCs. Compared with control group, the incidence of PPCs was significantly decreased (before matching: 42.7% vs. 35.2%, P=0.004; after matching: 42.2% vs. 35.6%, P=0.033), the incidence of acute kidney injury was decreased and no significant differences were found in the length of stay in intensive care unit, length of hospital stay and incidence of other adverse events in ulinastatin group ( P>0.05). In the extended Cox proportional hazard model before and after adjustment for confounding factors, the risk of PPCs was significantly reduced after the use of ulinastatin ( HR value before adjustment was 0.81, 95% confidence interval [ CI] 0.67-0.99, P=0.004; the HR value after adjustment was 0.79, 95% CI 0.65-0.96, P=0.022). The risk of PPCs was significantly decreased in patients aged >65 yr and at high risk of PPCs after using ulinastatin ( HR=0.667, 95% CI 0.542-0.821, P<0.001; hR value was 0.641, 95% CI 0.516-0.812, P<0.001). Conclusions:The intraoperative use of ulinastatin is helpful in decreasing the risk of PPCs in patients undergoing OPCABG.