Introduction: Surgery is linked with fear and stress that disrupt metabolic and neuroendocrine activities, which impair normal maintained glucose metabolism that leads to stress hyperglycaemia. This study aimed to compare the effect of general and spinal anaesthesia on perioperative blood glucose levels in patients undergoing lower abdominal and pelvic surgery. Methods: This prospective observational cohort study recruits 70 adult patients who underwent lower abdominal and pelvic surgery under general and spinal anaesthesia; 35 in each group. A systematic random sampling technique was used to select study participants. Capillary blood glucose was measured at four perioperative times. An independent t-test, dependent t-test, and Manny–Whitney U test were used for statistical analysis, as appropriate. P values less than 0.05 were considered statistically significant. Results: No statistically significant difference was observed in mean blood glucose levels at baseline and 5 min after induction of general anaesthesia and complete blocks of spinal anaesthesia. But at the end of surgery and 60 min after the end of surgery the mean blood glucose levels were statistically significantly higher in the general anaesthesia group compared with the spinal anaesthesia group (P<0.05). And the blood glucose level was significantly increased from baseline compared with the different time intervals in the general anaesthesia group. Conclusion: The mean blood glucose levels were lower in patients undergoing surgery under spinal anaesthesia compared with general anaesthesia. The authors recommend spinal over general anaesthesia whenever possible for patients undergoing lower abdominal and pelvic surgery.