Abstract: OBJECTIVE To investigate the characteristics and trends of postoperative nosocomial infection in patients of cardiac surgery department so as to provide bases for developing prevention measures. METHODS A total of 19 392 patients who received surgical procedures in cardiac surgery department of West China Hospital of Sichuan University from 2018 to 2022 were recruited as the research subjects. The nosocomial infection cases were prospectively monitored, the sites of postoperative nosocomial infection, pathogens and trend of infection were analyzed. RESULTS Among the 19 392 cardiac surgery departments who underwent surgical procedures, 330 (348 case-times) patients had nosocomial infection, with the infection rate 1.70%, the case-time infection rate 1.79%; the incidence of the postoperative infection showed an upward trend in the 5 years (P<0.001). The respiratory tract, blood system, urinary tract and surgical site were the major sites of postoperative infection. The incidence rates of lower respiratory tract infection postoperative pneumonia, blood system infection and urinary tract infection showed upward trends in the 5 years (P<0.05); there was no significant difference in the incidence of surgical site infection among the 5 years. Totally 347 strains of pathogens were isolated in the 5 years, the gram-negative bacteria were dominant among the pathogens, and Acinetobacter baumannii and Klebsiella pneumoniae were the predominant species; Staphylococcus aureus was the major species of gram-positive bacteria. Totally 48 strains of drug-resistant bacteria were isolated, and the constituent ratios of the drug-resistant strains were increased year by year (P<0.05). CONCLUSION The incidence of postoperative nosocomial infection is not high among the patients of cardiac surgery department but shows an upward trend. It is necessary to take effective prevention measures for the related risk factors and focus on the prevention and control of the postoperative pneumonia and blood infection. The constituent ratios of drug-resistant bacteria are increased year by year, and it is necessary to strengthen the reasonable use of antibiotics.