Background:The combination of adjuvants to local anesthetic is synergetic for producing the analgesia of prolonged duration without measurably increasing sympathetic or motor blockade. The present study was conducted to compare the different doses of nalbuphine as an adjuvant in patients undergoing surgery under sub arachnoid block with 0.5% hyperbaric Bupivacaine. Materials&Methods:Patients in Group A received 3 ml of 0.5% hyperbaric bupivacaine with 0.4mg Nalbuphine in 1ml Saline.Patients in Group B received 3 ml of hyperbaric 0.5% bupivacaine with 0.8mg of Nalbuphine in 1ml saline.The patients was observed for onset of sensory blockade; the height of sensory blockade, motor blockade as per bromage scale, total duration of sensory and motor blockade, quality of analgesia, two segment sensory regression time, time to first rescue analgesia and the number of rescue analgesics in 24 hrs. The data was analysed statistically using student t test, Chi-Square test. A P value less than 0.05 was considered statistically significant. Results:Mean heart rate of patients in the two study groups was found to be statistically non- significant at 40- & 60-minutes time interval. Mean systolic blood pressure of patients in the two study groups was found to be statistically non- significant at 120 minutes time interval. Mean diastolic blood pressure of patients in the two study groups was found to be statistically non- significant at 20-40 minutes and after 60 minutes time interval. Mean blood pressure of patients in the two study groups was found to be statistically non- significant at 10-20 minutes, 50- & 90-minutes time interval. Mean respiratory rate of patients in the two study groups at was found to be statistically significant (p<0.01). Mean saturation level of patients in the two study groups was found to be statistically non- significant at 10-40 minutes and post 90 minutes time interval. Mean pain score of patients in the two study groups was found to be statistically non- significant after 90 minutes time interval. Mean Time for Motor Block, Mean duration of surgery between two study groups was found to be statistically significant. Mean time for sensory block between two study groups was found to be statistically non-significant. Conclusion:The present study concluded that d 0.4 mg can be recommended as the optimal dose of nalbuphine if used intrathecally along with 3ml 0.5% hyperbaric bupivacaine in patientsundergoing various infra umbilical surgeries.