The aim of this study was to evaluate the safety of carbohydrate intake 2 hours before surgery in elderly patients undergoing free flap surgery for oral cancer. Elderly patients undergoing free flap surgery between September 2019 and January 2021 were randomly divided into control (n = 43) and intervention (n = 43) groups. Control group patients fasted for 6 hours and were forbidden from drinking water for 4 hours before surgery. Intervention group patients fasted for 6 hours and were forbidden from drinking after the oral administration of 5 ml/kg carbohydrate (≤400 ml) 2 hours before surgery. The main outcome measures were aspiration, fasting blood glucose level, insulin concentration, insulin resistance index (fasting at admission, prior to anaesthesia induction, immediately after surgery, and at 6 a.m. on postoperative days 1 and 2), and comfort before and after surgery. No aspiration occurred in any of the patients during anaesthesia. There were significant differences in fasting blood glucose, insulin concentration, and insulin resistance index between the control and intervention groups prior to anaesthesia induction, immediately after surgery, and on day 1 after surgery (P < 0.01). Thirst (P = 0.001) and hunger (P = 0.003) differed significantly between the two groups prior to anaesthesia induction. The intake of oral carbohydrate 2 hours before surgery was both safe and effective for elderly patients with oral cancer undergoing free flap surgery and could relieve the physiological stress response.