Background: Surgical site infection (SSI) remains one of the most common postoperative complications, particularly in cases involving contaminated or dirty abdominal surgeries. Despite improved aseptic techniques and antibiotic prophylaxis, SSI continues to contribute significantly to morbidity, prolonged hospitalization, and increased healthcare costs, especially in developing countries. Intraoperative intraperitoneal antibiotic lavage, particularly using gentamicin, has been proposed as an effective adjunct to reduce microbial contamination and postoperative infection risk. Objective: The present study aimed to evaluate the effect of intraperitoneal gentamicin lavage on postoperative surgical site infection (SSI) in children undergoing dirty laparotomy. Methods: This randomized controlled trial was conducted at the Faculty of Pediatric Surgery, Bangladesh Shishu Hospital and Institute, Dhaka, from March 2018 to December 2019. A total of 70 children (≤5 years) undergoing laparotomy for dirty surgery were randomly divided into two groups. Group A (n=35) received intraperitoneal lavage with gentamicin diluted in normal saline (160 mg/500 ml), whereas Group B (n=35) received lavage with normal saline only. Postoperative outcomes, including fever, wound infection, wound dehiscence, secondary closure, and hospital stay duration, were recorded and analyzed using SPSS version 23. Results: The groups were comparable in age and gender distribution (p>0.05). Postoperative fever occurred in 54.3% of Group A and 77.1% of Group B (p=0.044), while wound infection rates were significantly lower in the gentamicin group (11.4%) than in the control group (31.4%) (p=0.041). Although wound dehiscence and secondary closure did not differ significantly between groups, the mean postoperative hospital stay was notably shorter in Group A (8.17 ± 2.70 days) compared to Group B (10.71 ± 3.89 days) (p=0.002). Conclusion: Intraperitoneal gentamicin lavage significantly reduced postoperative fever, wound infection rates, and hospital stay duration in children undergoing dirty laparotomy. These findings suggest that gentamicin lavage can serve as an effective adjunctive measure to minimize postoperative infectious morbidity and enhance recovery in pediatric contaminated abdominal surgeries.