The conduction velocity of red and white muscle fibers were measured by intracellular microelectrode techiuigue and the differences of conduction velocities between these two fibers were demonstrated. Materials wereused the M. soleus of rat as a red fiber preparation and the outer surface part of M. rectus femoris as a white muscle fiber preparation. 1. Conduction velocities of red muscle fibers were slower than thase of white muscle fibers. (1) Conduction velocity of red muscle fiber. The first case; 1.81±0.52m/sec. The second case; 2.61±0.68m/sec. The third case: 2.25±0.48m/sec. (2) Conduction velocity of white muscle fiber. The first case; 3.43±0.95m/sec. The second case: 5.57±0.88m/sec. The third ease: 4.74±0.73m/sec. 2. It was widely known that the conduction velocity of muscle fider was in the proportion to the root of fiber diameter. There was no obvious difference of fiber diameters between the white fibers in surface part of M. rectus femoris and the red fibers in M. soleus. 3. So it may be reasonably concladed the difference of conduction velocity between the red and white muscle fiber was not depend upon the differences of their diametsr.