Background: Diabetes mellitus may affect corneal endothelial health, potentially impacting outcomes of cataract surgery.Objective: To compare changes in corneal endothelial cell count and central corneal thickness (CCT) after manual small incision cataract surgery (SICS) in patients with and without diabetes.Methods: This prospective study included 50 diabetic and 50 non-diabetic patients undergoing manual SICS. Corneal endothelial cell density and CCT were measured preoperatively and at day 1, week 1, and month 1 postoperatively. Results: At one month post-surgery, diabetic patients showed significantly greater endothelial cell loss (14.6% vs. 10.3%, p=0.003) and CCT increase (2.2% vs. 1.1%, p=0.025) compared to non-diabetic patients. Age (β=-5.2, p=0.004), presence of diabetes (β=-78.3, p=0.002), and HbA1c levels (β=-28.7, p=0.012) were significant predictors of endothelial cell loss. Visual acuity outcomes were similar between groups (0.18 ± 0.12 vs. 0.15 ± 0.10 logMAR, p=0.161), but diabetic patients showed a trend towards more complications. Conclusion: Diabetic patients experience greater corneal endothelial cell loss and increased CCT following manual SICS compared to non-diabetic patients. These findings highlight the need for careful consideration of diabetes in preoperative assessment and postoperative management of cataract surgery patients.