Adjuvant drugs are used to prolong the analgesic effects of local anesthetics in regional nerve blocks. This study was done to show the efficacy of Dexamethasone as a potent adjuvant in Supraclavicular Brachial plexus block. 60 patients who underwent upper limb surgeries were chosen for supra clavicular brachial plexus block and randomly allocated to two equal groups,one to receive Dexamethasone and the other to receive normal saline along with Lignocaine Bupivacaine mixture. Time of onset and duration of motor and sensory blockade were noted. The quality of Anesthesia and occurrence of complications was also observed.The mean onset time of sensory blockade in group A is 19.30, and in group B is 16.43 minutes. (p<0.005). The mean onset time of motor blockade in group A is 15.13 minutes, in group B is 13.33 minutes (p<0.005). In group A the quality of Anesthesia is 3 for 26 patients, 2 for 4 patients and in group B it is 3 for 29 patients and 2 for 1 patient. Statistical analysis shows the p value is 0.161, which is not significant. The mean duration of motor blockade in group A is 207.67 minutes, in group B is 374.93 minutes (p<0.005). The mean duration of sensory blockade in group A is 318.77 minutes, in group B is 642.33 minutes (p<0.005). There were no complications reported. We conclude that addition of dexamethasone to local anesthetic mixture fastens the onset of action of motor and sensory blockade, and prolongs the duration of motor blockade and analgesia significantly.