Objective To evaluate the usefulness of tip perfusion index(TPI) changes for objective prediction of successful brachial plexus block. Methods seventy ASA I-II patients scheduled for upper extremity operation under brachial plexus block were included in the study.Noninvasive arterial blood pressure, electrocardiogram, bilateral upper extremity oxygen saturation and TPI values were measured. Operating room temperature was controlled between 24-26℃. Midazolam 0.06 mg.kg-1 was given IV at 10min before blockade.The onset time of analgesia in blocked upper limb and TPI values of bilateralis upper limb were recorded. Results There was no change in TPI values in the unblocked upper limb after successful Axillary/ Interscalene approach brachial plexus block. In the successful axillary approach brachial plexus block group, PFI values in blocked upper limb started to statistically significant increase as early as 8 min after the local anesthetic was injected compared to unblocked upper limb. In the successful Interscalene approach brachial plexus block group, PFI values in blocked upper limb started to statistically significant increase as early as 6 min compared to unblocked upper limb. There was no recorded statistically relevant increase in TPI values in a 30-min period in the failed block patients. Conclusion PFI provides a simple, early, noinvisive ,and objective assessment of the success and failure of brachial plexus block nerve blocks compared to traditionary pinprick method.