Objective : Electrodiagnostic test has shown diagnostic sensitivity and specificity in carpal tunnel syndrome[CTS]. This study was to evaluate the correlation between clinical outcome of endoscopic carpal tunnel ligament release[ECTR] and the predictive value of sensory nerve conduction. Methods : From January 1998 to December 2004, 87 patients [44 right hand, 37 left hand, 6 bilateral hands] with CTS who underwent ECTR were followed up in our hospital for an average of 24 months. We retrospectively analyzed the results with previous medical records. All patients underwent electrodiagnostic test and ECTR. The patients were divided into three groups according to the electrodiagnostic test results. Group [A] was normal sensory nerve response, Group [B] was slowing sensory response and Group [C] was no sensory response. Improvement of the symptom after ECTR was assessed using a visual analogue scale[VAS] score. Results : Differences between the three groups on the correlation of severity of sensory potential and duration of preoperative symptoms were significant. The mean value of improved VAS scores for the three groups were $6.0{pm}0.96$ in the Group A, $6.11{pm}0.48$ in the Group B and $6.14{pm}0.53$ in the Group C. There was no statistically significant difference between the severity of sensory nerve response and improvement in VAS score after ECTR. Complications included a wound infection, a case of skin necrosis, and two patients with persistent symptoms without any improvement. Conclusion : Although electrodiagnostic test has been known to be useful, sensory nerve response is considered not to be a good prognostic value for carpal tunnel syndrome after ECTR.