It is widely blieved that the new bone formation is provoked by fine electrical stress to bone. There have been maay experimental studies that showed much efforts to define these small amounts of electricity, and these fine electricities are being used in the orthopedic field for the treatment of various fractures, nonunions and pseudsrthrosia The auther has checked the electrical potentials changing in the course of fractvre hesling in rabbits femur. Comparing these data with that of the normal control group, the following results were obtained. 1. In the normal rabbit's femur the electrical potentisl was 13.6mV less on the concave side than on the convex side. This finding can be explained by the existence of stress generated potential or piexoelectricity. 2. Electrcal potentials on the fractured femoral sites were lowered significantly from that of the control group. So auther could confirm the existence of bioelectrical generated by increased electrical activity of the living bone. 3. The electrical potential of the fractured femoral site has been decreased 50% and 20% as low as that of the normal site at 8 weeks respectively. It is expected that these lowered electrical potentials may become dose to the normal values when the changed metabolic process due to the fractured bone is no longer functioning and it is believed to take human 2 years to get the normal value.