Abstract: Objective: To evaluate the efficacy and safety of sufentanil in patient-controlled intravenous analgesia(PCIA) for patients with thoracotomy through pain assessment and monitoring of respiration. Methods: Fifty-three patients (ASA Ⅰ~Ⅱ) with thoracotomy were divided into 2 groups: the sufentanil group (group S, n=25) and the fentanyl group (group F, n=28). In group S the background infusion of sufentanil was 0.03μg/kg·h and the bolus dose was 0.03 μg/kg with a locktime of 15 minutes. In group F the background infusion of fentanyl was 0.3μg/kg·h and the bolus dose was 0.3 μg/kg with a locktime of 15 minutes. VAS and 6-point Ramsay scale were used to evaluate the analgesic response and sedation. The cumulative dosage consumed each day and any adverse effects were recorded. Results: The satisfactory analgesic ratio in group S and group F was 88.0% and 89.3%, respectively, with no significant difference between the two groups (P>0.05). The cumulative volume consumed in group S on the first, second, and third day was higher than that in group F (P<0.05). There was no statistically significant difference in VAS and Ramsay scale between the two groups (P>0.05). Adverse effects like respiratory depression, postoperative nausea and vomiting were slight, and there was no significant difference between the two groups (P>0.05). Conclusion: Used in PCIA in patients undergoing thoracotomy, sufentanil provides satisfactory postoperative analgesia with convenient application and good haemodynamic stability. It is safe to use sufentanil provided patient respiration and state of consciousness are monitored.