Objective: To assess the efficacy and adverse effects of fentanyl intravenous (IV) patient-controlled analgesia (PCA) compared with morphine IV-PCA in patients after major abdominal surgery. Methods: In a prospective, randomized, observer-blinded study, 40 patients with ASA physical status I-II who were scheduled to undergo major abdominal surgery. A standard general anesthetic was administered. Patients were randomly divided into two groups for 24h postoperatively: 1) Group F with fentanyl concentration of 25 μg/mL, background infusion of 25 μg/h, bolus of 25 μg, and lockout time of 10 min; and 2) Group M with morphine concentration of 1 μg/ml, no background infusion, bolus of 1 mg, and lockout time of 10 min. Numerical rating scale (NRS) pain scores at rest and on coughing and dose of additional PCA bolus and supplemental analgesic, and the incidence of adverse effects were assessed postoperatively during the first 24 h postoperatively. Results: Compared to Group M, Group F showed significantly lower postoperative pain scores at rest throughout the observation period and on coughing at 2 h after the end of surgery. Incidence of nausea and median dose of antiemetic drugs were comparable between groups. No respiratory complications were encountered in this study. Patient satisfaction scores were significantly higher in Group F than in Group M. Conclusions: Fentanyl IV-PCA provides more effective postoperative pain relief than morphine IV-PCA and greater patient satisfaction after abdominal surgery, without increasing the incidence of adverse effects.