Abstract: Objective To evaluate the clinical efficacy of sufentanil and fentanyl at equivalent dose for patient-controlled intravenous analgesia (PCIA) after thoracotomy. Methods Sixty ASA Ⅰ-Ⅱ patients (20-60 years of age) undergoing radical operation for lung or esophageal cancer were randomly divided into sufentanil intravenous analgesia group (group S, with sufentanil 1 μg/ml) and fentanyl intravenous analgesia group (group F, fentanyl 10 μg/ml). PCIA was administered with background infusion of 2.5 ml/h , bolus injection of 2.5 ml and lockout time of 15 min. The pain intensity according to visual analogue scale (VAS), cumulative analgesic consumption (CAC), sedative scores and side effects at 24 and 48 h after administration were recorded. SpO2, respiratory rate (RR), blood pressure (BP) and ECG were continuously monitored. Results There were no significant differences in CAC between the two groups, but he VAS was lower in group S than in group F (P<0.05) and the sedative efficacy was superior in group S (P<0.05). The incidence of nausea and vomiting in group S was lower than that in group F (P<0.05). No significant differences were observed in SpO2, RR, heart rate and mean arterial pressure between the two groups. Conclusion PCIA with sufentanil provides better efficacy of analgesia and sedation with lower incidence of nausea and vomiting than with fentanyl in postoperative patients with thoracotomy.