Background: brachial plexus block is a common technique instead of general anaesthesia. This type of anaesthesia primarily assists in achieving the best possible operating conditions by causing muscular relaxation, maintaining a stable intraoperative hemodynamic condition, and inducing sympathetic block, which lessens postoperative discomfort, vasospasm, and edoema. Aim & Objective:1. To compare the duration of post operative analgesia 2. To compare the onset & duration of sensory and motor block, hemodynamic changes and adverse effects. Methods: Study design: Randomized comparative study. Study setting: Department of Anaesthesia, Kamineni Institute of Medical Sciences, Sreepuram Narketpally, India. Study duration: From January 2021 to July 2022 (1.5 year). Study population: All patients undergoing upper limb surgeries (below shoulder) under brachial plexus block by supraclavicular approach. Sample size: 105. Results: Age distribution across groups was found statistically significant (p=0.033). This infers that age has a significant impact in causing the variation in results across various groups. mean duration of sensory block measured by return of pin prick sensation was 11.537 hours, 7.81 hours and 10.048 hours in groups A, B and C respectively. p-value was statistically significant (<0.001). mean duration of motor blockade was 9.784 hours, 7.05 hours and 8.774 hours in groups A, B and C respectively. p-value was statistically significant (<0.001). mean duration of effective analgesia (VAS>4) was 14.221 hours, 9.583 hours and 12.299 hours in groups A, B and C respectively. p-value was statistically significant (<0.001). mean duration of complete analgesia (VAS>0) was 11.537 hours, 7.81 hours and 10.048 hours in groups A, B and C respectively. p-value was statistically significant (<0.001). Conclusion: dexmedetomidine is a better option than fentanyl when used for supraclavicular block techniques along with bupivacaine and lignocaine.