The present paper was done to review common diagnostic techniques used to help surgeons find the most suitable way to diagnose postoperative intra-abdominal sepsis (IAS). The topic was searched on MEDLINE, Embase, and Cochrane Library databases. Collected articles were classified and checked for their quality. Findings of selected research were included in this study and analyzed to find the best diagnostic method for intra-abdominal sepsis. IAS presents severe morbidity and mortality, and its early diagnosis can improve the outcome. Currently, there is no consensus among surgeons on a single diagnostic modality that should be used while deciding reoperation in patients with postoperative IAS. Though it has a high sensitivity for abdominal infections, computed tomography has limited applications due to mobility and time constraints. Diagnostic laparoscopy is a safe process that produces usable images, and can be used at the bedside. Diagnostic peritoneal lavage (DPL) has high sensitivity, and the patients testing positive through DPL can be subjected to exploratory laparotomy, depending on severity. Abdominal Reoperation Predictive Index (ARPI) is the only index reported as an aid for this purpose. Serial intra-abdominal pressure measurement has also emerged as a potential diagnostic tool. A proper selection of diagnostic modality is expected to improve the outcome in IAS, which presents high mortality risk and a limited time frame.