Background: Brachial plexus block provides excellent anaesthesia and analgesia for upper limb surgeries. It was found that when dexamethasone was added as an additive to local anaesthetic agent, it shortens the onset of sensory and motor blockade. This study was carried out to compare the onset of sensory and motor blockade on addition of dexamethasone to local anaesthetics versus local anaesthetics only in supraclavicular brachial plexus block. Materials and Methods: This was a prospective, randomized and controlled study conducted on 60 ASA class I & II physical status patients undergoing elective upper limb surgery after obtaining approval of Institutional Ethics Committee. After written informed consent, patients were randomly allocated to two groups i.e. Group A and Group B of 30 each. Group A (control) received lignocaine with adrenaline 14 ml and bupivacaine 16 ml. Group B (study) received lignocaine with adrenaline 14 ml and bupivacaine 16 ml along with dexamethasone 4 mg. Time for onset of sensory and motor blockade was recorded. Result: The average age of the patients was 33.401±9.1 years in Group A and 35.101±6.8 years in Group B. The average weight of the patients was 60.411±3.4 kg in Group A and 63.349±4.1 kg in Group B respectively. Both groups had predominantly male patients accounting for nearly two third of the total study population in each group. The difference in age, weight and sex distribution was statistically insignificant. The observed average time for onset of sensory blockade was 10.18±0.87 minutes in Group A and 8.24±0.72 minutes in Group B. The average time for onset of motor blockade was 12.11±3.52 minutes in Group A and 10.51±2.38 minutes in Group B. Conclusion: Dexamethasone when added to local anaesthetic agents in supraclavicular brachial plexus block significantly shortens the onset of sensory and motor blockade without any untoward side effect.