The piezoelectric effect of bone has been observed similarly to the case of wood or ramie. The specimens were cut out from the femur of man and ox, and dried completely by heating. The piezoelectric constants were measured by three different experiments, that is, measurements of the static direct effect, the dynamic direct effect and the dynamic converse effect. The piezoelectric effect appears only when the shearing force is applied to the collagen fibres to make them slip past erch other. The magnitude of piezoelectric constant depends on the angle between the applied pressure and the axis of the bone. The maximum value of piezoelectric constant amounts to 6× 10-9 c.g.s. e.s.u., which is about one-tenth of a piezoelectric constant d11 of quarts crystal. The specimens which were boiled in hot water and afterwards dried completely showed little change in the piezoelectric effect, the fact ascertaining that the effect is not of biological origin. The origin to piezoelectricity in bone may be ascribed to the piezoelectric effect of the crystalline micelle of collagen molecules. The consideration of the symmetry of the configulation of collagen fibres in the bone texture shows the existence of effects which are represented by only two piezoelectric constants d14 and d25, which are the same in magnitude but opposite in sign.