Objectives <p>The aim of this study is to evaluate the utilization of intraoperative colonoscopy (IOC) for determining the integrity of the anastomosis and to establish an IOC scoring system.</p> Methods <p>A retrospective cohort study was conducted from January 2021 to June 2024, we analyzed the clinical data of 160 patients registered in a database who underwent laparoscopic left-sided colectomy at Pusan National University Yangsan Hospital. IOC was performed on all patients, and Mucosal color (MC), stapled line bleeding (BL), proximal redundancy (PR), and bowel preparation (BP) were evaluated and scored as variables. Logistic regression analysis was used to evaluate risk factors for anastomotic leakage (AL) and Cohen's kappa was applied to assess the reproducibility of the evaluation.</p> Results <p>Of 160 patients, 10 (6.25%) experienced AL. All the IOC variables had kappa values of 0.8 or higher, indicating good agreement. The logistic regression analysis revealed significant differences in the MC 2 (<i>P</i> = 0.017, OR 12.86), PR 2 (<i>P</i> = 0.001, OR 27.64), BP 2 (<i>p</i> = 0.016, OR 10.50) PR 2 score (<i>P</i> = 0.016, OR 10.50) and the sum of the scores (<i>p</i> = 0.001, OR 3.51).</p> Conclusion <p>IOC can be performed as a reference procedure to assess the integrity of the anastomosis during left-sided colorectal surgery.</p>