Background: Upper extremity surgeries are being mostly done under regional anesthesia using supraclavicular brachial plexus block under ultrasound guidance. Subjective methods to assess the block success take time and are not very reliable. Aims- To use perfusion index values for prediction of successful ultrasound guided supraclavicular brachial plexus block. Materials and methods- This prospective observational study was done on 70 patients who underwent upper limb surgery. Ultrasound guided supraclavicular block was given using 20 ml of 0.5% ropivacaine in all patients. Assessment of sensory and motor block was done at every 5 minute interval. The perfusion index was noted at baseline and at 5, 10, 15, 20, 25 and 30 minutes using separate pulse oximeters on index finger of both blocked and unblocked upper limbs. The perfusion index (PI) ratio was calculated as ratio of PI at 10 minutes and PI at baseline. Results- There was increase in perfusion index (PI) and PI ratio in the blocked arm compared with the unblocked arm with statistically significant difference. Conclusion- Perfusion index (PI) and PI ratio at 10 min are good predictors of success of supraclavicular block which can be used non invasively in all patients.