Spinal anaesthesia is one of the most commonly used technique for lower abdominal and lower limbs surgeries. However its short duration of action and early arising post-operative pain moves the focus towards the use of adjuvant to it. So numbers of adjuvant from different groups were used and evaluated. Out of which opioids are the most commonly used family as an intrathecal adjuvant to local anaesthetics. Our aim of the study to evaluate the analgesic efficacy of hyperbaric Bupivacaine & Nalbuphine versus hypebaric Bupivacaine & Fentanyl in infraumbilical surgeries. The study was conducted during period of 2020 to 2022 at tertiary care center. Total 100 patients were participated in study each group includes 50. Demographic data, onset of sensory & motor block, duration of sensory and motor block, two segment regression time and first rescue analgesia time were noted. The onset of sensory and motor block was earlier in Bupivacaine plus Nalbuphine (BN) combination as compared to Fentanyl plus Bupivacaine (BF) combination. Two segment regression time was longer with BN group. Nalbuphine also shows good hemodynamic stability. Rescue analgesia time with Nalbuphine was much longer than Fentanyl. The adverse effect was also much less with Nalbuphine. Nalbuphine could be a better and settle alternative to the Fentanyl and other opioids as adjuvant to intrathecal local anaesthetics.