Aim: to compare the effectiveness and safety of transdermal buprenorphine with the widely used parenteral analgesic, diclofenac, for postoperative analgesia in the setting of major upper abdominal surgery under general anesthesia (GA). Material and Methods: This was prospective, controlled clinical trial done in the Department of Anesthesia, ICARE Institute of Medical Science and Research &Dr.Bidhan Chandra Roy Hospital, Haldia,West Bengal, India. Patients were allocated to two parallel study groups by simple, balanced randomization using a computer-generated random number list. One group received buprenorphine patch releasing 20µg/h. The other group received diclofenac sodium intramuscular (IM) injection, in aqueous solution, 75 mg in the deltoid region. The primary outcome measure was postoperative pain assessed by VAS scoring at 4-h intervals for the first 12 h and then 12 hourly till the end of 72 h. For VAS scoring, a 10 cm vertical line was used, marked out in millimeters. The number of episodes of nausea-vomiting (despite postoperative ondansetron 4 mg 8-hourly for 48 h) was noted. Changes in vital parameters and other potential treatment-emergent adverse events were recorded The target sample size was 50 evaluable patients in each group. Results: In the buprenorphine group, although the VAS score declined over time, the reduction attained statistical significance in comparison to the baseline (4 h) VAS score only at 72 h. In contrast, in the diclofenac group, VAS score achieved a statistically significant reduction in comparison to baseline from 8 h onwards, and this was maintained until the end of the observation period. In the buprenorphine group, 31 patients (62%) required rescue analgesia within the 72 h observation period, in contrast to 12 (24%) in the diclofenac group. This difference was statistically significant (P = 0.012). Conclusion: we concluded that the primary outcome measure was comparable between the groups, the pattern of rescue analgesia use suggests that postoperative analgesia experience with buprenorphine patch was less satisfactory than diclofenac injection in this study.