Background: Spinal anaesthesia requires a small volume of drug to produce profound sensory and motor blockade but has limited duration of action. An adjunct to local anaesthetic produces a better-quality regional block. The present study was aimed to evaluate the study and tolerability of combined use of intrathecal neostigmine and fentanyl as an adjunct to bupivacaine for postoperative analgesia in patients posted for abdominal surgeries under spinal anaesthesia. Material and Methods: Present study was single-center, prospective, comparative, observational study, conducted in patients of age group of 20-60 years, of either gender, ASA grade I/II, Elective patients undergoing Lower Abdominal Surgeries. 60 patients were divided by computer assisted randomization table into 2 groups of 30 subjects each as GROUP B (BUPIVACAINE Group) & GROUP C (COMBINED Fentanyl Neostigmine Group). Results: There was no significant difference in age distribution, gender distribution & ASA grade in two groups. (p>0.05). The mean duration of sensory block was found to be 194.16 ±21.43 minutes in group C while 153.03 ±19.19 minutes in group B, difference was statistically highly significant. (P <0.0001). The mean duration of motor block was found to be 197.18 ±21.78 minutes in group C while 169.26 ± 19.38 minutes in group B, difference was statistically highly significant. (P <0.0001) There was no difference when two groups were compared statistically for complications. (p>0.05) post-operative analgesia remained for longer duration in Group C, 7.40 ± 1.21 hours as compared to 5.32 ± 1.21hours in Group B, difference was statistically significant (P <0.05). Conclusion: Spinal neostigmine added to bupivacaine and fentanyl provided a significantly longer surgical analgesia and insignificant adverse effects who had lower abdominal surgery under spinal anaesthesia.