This paper reports design, fabrication and measurement results of a flexible microelectrode array for monitoring compound nerve action potential (CNAP) of a peripheral nerve. For building electrical nerve-signal-database up, the flexible microelectrode array was fabricated through a ‘polymer/metal multilayer processing technique’ on a silicon wafer, and it was released by chemical ‘etch-release’ scheme which results in no mechanical stress on the device. In vitro test had been conducted to examine interfacial impedance and signal transfer characteristics. The interfacial impedance was 420Ω/μm 2 at 1 kHz. In vivo test had been carried out by implanting an assembly (composed of microelectrode array and a polygloycolic acid conduit) into a sciatic nerve of 10 male rats where nerve defect was 6 mm. after 3 month-implantation periods, sciatic nerve function was tested with gait analysis, and CNAP by using a bio-amplifier which was developed soley for this application. From the gait analysis, it was ascertained that nearly half of the original functions was restored, which is backed up by sciatic nerve function index (SNFI), -48.5±15.0. CNAP of the regenerated nerve through the proposed microelectrodes was examined through transmission electron microscope (TEM) images. From the TEM images, it was confirmed that proximal and distal nerve showed nearly same morphology and axon number.