Background: The proper management of postoperative pain improves patients’ quality of life, accelerates early postoperative recovery, shortens hospitalization period, and reduces medical costs. This study aimed to compare the effectiveness of intravenous fentanyl pump and sublingual buprenorphine tablet in controlling pain after open cholecystectomy. Objectives: Evaluating the effectiveness of sublingual buprenorphine in reducing postoperative pain and complications after open cholecystectomy. Methods: This study was a double-blind, randomized clinical trial. The study population encompassed those candidates undergoing open cholecystectomy, patients with ASA class I and II, individuals undergoing no other concomitant surgery, and patients in the age range of 20 - 50 years. The first group received sublingual buprenorphine 6, 12, and 18 hours after the first administration. The second group received fentanyl as patient-controlled analgesia (PCA) for 24 hours. Then nausea, vomiting, sedation, and Visual Analog Scale (VAS) scores were evaluated at the beginning, 2, 6, 12, 18, and 24 hours after surgery. The collected data were analyzed using SPSS software version 20. Results: The mean age of the patients in the buprenorphine and fentanyl groups were 44.8 ± 5.5 and 42.8 ± 7.1 years, respectively. In this study, 22.5% of the patients in the buprenorphine group and 35.5% of the patients in the fentanyl group were male. During 6 and 24 hours after surgery, the pain level regarding the VAS scores was significantly lower in the buprenorphine group than in the fentanyl group; however, analgesic consumption was higher in the fentanyl group. In the early hours after surgery (2 and 6 hours), nausea and vomiting were lower in the buprenorphine group than in the fentanyl group even though the difference was not significant. Conclusions: This study suggests buprenorphine as an effective drug for patients to reduce postoperative pain because of its limited complications, inexpensiveness, and more convenient administration method.