INTRODUCTIONSurgical site infections (SSIs) are significant postoperative risks; antibiotic prophylaxis is crucial due to the presence of anaerobic bacteria. This study investigated the efficacy and safety of a novel nitroimidazole, morinidazole, in SSI reduction in class III wounds, as there is currently a lack of evidence in the existing literature.METHODSA multi-centre randomized clinical trial was conducted from December 2020 to October 2022 in the general surgery departments of 12 tertiary hospitals in China, including 459 patients in two treatment groups using morinidazole plus ceftriaxone or ceftriaxone alone. Efficacy and safety were evaluated including SSI incidence, adverse events, and compliance. Statistical analysis employed SAS 9.4 software. Data analysis was performed from February to May 2023.RESULTSA total of 440 participants (median (interquartile range, IQR) age, 63.0 (54.0, 70.0) years; 282 males (64.09%); 437 patients were of Han race (99.32%) and were randomized. The experimental group exhibited a significantly lower SSI rate compared with the control group (31 (14.49%) vs 52 (23.01%); risk difference, 1.76%, 95% confidence interval (CI) 1.08-2.88%; P=0.0224). The superficial incisional site infections revealed a marked reduction in the experimental group (12 (5.61%) vs 31 (13.37%); risk difference, 2.68%; 95% CI 1.34-5.36%; P=0.0042). Non-surgical site infections, severe postoperative complications, and total adverse events showed no statistically significant differences between the groups (P>0.05).CONCLUSIONThe significant decrease in SSI rates and superficial incisional infections demonstrates morinidazole to be a valuable prophylactic antibiotic. Our findings provide valuable insights for clinical practice, where this new-generation nitroimidazole can play a crucial role in SSI prevention.