The both legs of 109 subjects(52 male and 57 female) were tested electrophysiologically for the presence of accessory deep peroneal nerve(ADPN). The incidence of ADPN was 36% of subjects and 23% of total tested legs A detected bilaterally in 11% of subjects. The average amplitude of compound muscle action potential(CMAP) evoked by the stimulation of ADPN was 0.7mV and the average ADPN innervation ratio(AIR) was 1096. The amplitude of CMAP evoked by stimulation was highly correlated with the AIR. The ADPN had significant influence on the physiologic conduction block; in 25 of the 51 ADPN-detected legs, the amplit CMAP evoked by the stimulation at the knee was same or higher than that at dorsum of ankle.