Background: Healthcare associated infection (HAI) poses major problem for doctors as well as patients and community at large. Among health care associated infections, surgical site infections are the second most common after urinary tract infection. Aim: The aim of the present study was to identify bacterial aetiology of surgical site infections. Material and methods: The study was a prospective, observational study which was carried in the Department of Microbiology, MGM Medical College and LSK Hospital, Kishanganj, Bihar, India.from February 2019 July 2020. A total of 390 patients with clinically diagnosed surgical site infection were chosen for the study. Suitable specimens from all these patients were subjected to Gram staining and culture on suitable culture media, and isolates were identified by colony characters and the battery of standard biochemical tests. All the isolates were tested for antimicrobial susceptibility by Kirby Bauer disk diffusion technique on Muller Hinton Agar. Results: Out of 390 samples, 200 samples yielded positive culture (51.28%). Out of the positive samples Staphylococcus aureus (27.5%) was the most common pathogen isolated followed by Escherichia coli (22%), Citrobacter spp. (15%) and Pseudomonas aeruginosa (12.5%). Conclusion: We conclude that the surgical site infections caused by Gram positive and Gram negative bacteria continue to be a frequent complication of surgical interventions. As the increasing resistance to antimicrobials increases the risk of morbidity and mortality, there is an urgent need for implementation of measures to restrict the health care associated infections