Aim and Objectives: To assess the effect of dexamethasone on onset and duration of anaesthesia as well as duration of analgesia when added to local anaesthetic solution for supraclavicular brachial plexus block. Methods: A randomized comparative study included total 60 patients of either sex, age between 18-70 years belonging to ASA Grade I and II undergoing elective or emergency surgeries of upper limb under supraclavicular brachial plexus block. Patients were randomly divided in group A (40 ml volume of lignocaine 2% with adrenaline (1:200000) + 0.5% bupivacaine) and group B (40 ml volume of lignocaine 2% with adrenaline (1:200000) + 0.5% bupivacaine with dexamethasone 8 mg). The onset and duration of sensory and motor block as well as duration of analgesia in the two groups were compared and any complications of the procedure were noted. Result: Group B had early onset and prolonged duration of sensory and motor block as well as prolonged duration of analgesia as compared to group A. None of the patients had bradycardia, hypotension or any other side effects. Conclusion:We concluded that addition of 8 mg dexamethasone to local anaesthetics in supraclavicular brachial plexus block reduces the time to onset of sensory and motor blockage and prolonged duration of postoperative analgesia.