This paper reports an implantable microelectrode for monitoring compound nerve action potential of a peripheral nerve that is regenerated form a severe injury, dissection in this case. The microelectrode is realized using a biocompatible polymer substrate (PI2611, HDMicrosystems) and the gold electrode. It may provide a new method for inspecting functions of a regenerated peripheral nerve while a current method is gait analysis that is a foot-print study. The microelectrode was separated from a carrier wafer by chemical 'etch-release' method inducing no mechanical stress on the device. The device separation method is advantageous for finer features and fabrication reliability because it can eliminate deformation of small features due to the mechanical stress. The proposed implantable had implanted into a sciatic nerve of a rat for 3 months, and compound action potential from the regenerated nerve was recorded through the microelectrodes.