Background: Pain poses a unique challenge to anesthesiologist. Continuous unrelieved pain activates the pituitary adrenal axis which can suppress the immune system resulting in postsurgical infection and poor wound healing. Opioids have been added as adjuvants to local anesthetics in spinal anesthesia to alleviate pain. Fentanyl is a phenylpiperidine derivative synthetic opioid agonist. As an analgesic fentanyl is 75-125 times more potent than morphine. Buprenorphine is an agonist antagonist derived from the opium alkaloid the baine. It is estimated that affinity of buprenorphine for mu receptors is 50 times greater than that of morphine. This study was carried out to evaluate the effects of Intrathecal Fentanyl with bupivacaine compared to intrathecal buprenorphine with bupivacaine on duration of post operative analgesia in lower abdominal surgeries. Methods: A double blinded randomised study was carried out with one hundred and thirty two patients of ASA grade I and II aged between 20 and 70 years undergoing lower abdominal and lower limb surgeries under spinal anaesthesia. The patients were given 3 ml of hyperbaric bupivacaine premixed with either 10 mcg Fentanyl (Group F), Buprenorphine 60 mcg (Group B) or 0.2 ml normal saline (Group S). Postoperatively VAS score for pain, time to first dose of analgesic required, total analgesic required and adverse effects with in 24 hours post operative period were noted. Results: Prolonged post operative analgesia was observed in Group BB (623.11 ± 98.86) compared to Group BF (536.56 ± 69.31) and BS (296.88 ± 36.32). Post operative rescue analgesic requirement was significantly less in group buprenorphine. Conclusion: Addition of Fentanyl and Buprenorphine as adjuvants to intrathecal 0.5% hyperbaric bupivacaine prolongs post operative analgesia. Intrathecal buprenorphine 60mcg as an adjunct to bupivacaine for subarachnoid block showed a longer duration of action and less postoperative rescue analgesic requirement in comparison to Intrathecal Fentanyl 10 mcg.