Background: Management of postoperative pain is essential for the smooth recovery of the patients. Intrathecal opioids are commonly used adjuvants to bupivacaine heavy for improving the quality of spinal anaesthesia. There are less number of studies comparing intrathecal butorphanol and pethidine. Aims: To compare the effects of intrathecal butorphanol versus pethidine on spinal anaesthesia produced by bupivacaine heavy.Settings and design: A prospective randomized double blind study. Materials and methods: 100 patients of ASA 1 & 2 undergoing spinal anaesthesia were randomly allotted to group A or B. Group A received intrathecal 0.5 mg butorphanol + 2.5 ml 0.5% bupivacaine heavy. Group B received intrathecal 25 mg pethidine + 2.5 ml 0.5% bupivacaine heavy. All patients were monitored for sensory and motor blockade, and occurrence of any side effects. Statistical analysis used: SPSS statistical software version 21.0. The mean and standard deviation computed for quantitative data. Proportions calculated for qualitative data. Appropriate test of significance used and a P value < 0.05 considered significant. Results: Mean time of duration of sensory blockade was 161.40 ± 12.291 minutes in group A and 147.10 ± 8.087 minutes in group B, which is statistically significant (p<0.001). Mean time of duration of analgesia was 304.70 ± 22.484 minutes in group A and 215.26 ± 16.359 minutes in group B, which is statistically significant (p<0.001). Neither of the groups had prolonged motor blockade or adverse effects. Conclusion: Intrathecal butorphanol and pethidine work synergistically with bupivacaine heavy to prolong the duration of sensory blockade and analgesia without prolonging the motor blockade and without causing any significant side effects. The effect is more pronounced with butorphanol compared to pethidine.