Objective To investigate the extent of electmphysiologic improvement of the two procedures of median nerve decompression after comparing the mid-to long-term electrophysiologic results of endoscopic and open carpal tunnel release of patients with intermediate to severe carpal tunnel syndrome.Methods The clinical data of 46 cases (59 wrists) of carpal tunnel syndrome (CTS) were treated in two groups according to the randomized operation mode,endoscopic carpal tunnel release (ECTR) group (32 wrists in 24 cases) and open carpal tunnel release (OCTR) group (27 wrists in 22 cases).Nerve conduction study was carried out to record compound muscle action potential (CMAP),sensory nerve action potential (SNAP) and sensory nerve conduction velocity (SNCV) one year after the carpal tunnel release.CMAP latency,SNAP amplitude and SNCV were analyzed and compared between the two groups.Results The differences in abductor policis brevis CMAP latency and SNCV one year postoperatively were of statistical significance between the ECTR group and the OCTR group.However,there were no statistically significant differences between the SNAP amplitudes of the two groups.Conclusion The mid-to long-term neuroelectrophysiologic results indicated that the improvement of electrophysiologic indices of conventional OCTR is better than those of the ECTR in treating intermediate to severe carpal tunnel syndrome.