Healthy bone has many physiological microcracks, which may be involved in the release of growth factors and act to accelerate bone remodeling process. In this study, the cortical bone fragments (5 x 5 x 1 mm³) from rat skull were ultrasonically demineralized with acidic electrolyzed water (AEW: pH 2.7) in ultrasonic bath (120 W, 38 kHz, 20 min) designated as ultrasonic bone. Fresh bone and ultrasonic bone were grafted into subcutaneous tissue of 4 week-old male rats, and explanted at 2 and 4 weeks. Fresh bone had physiological micro-cracks, while ultrasonic bone showed clear enlargement and union of cracks on SEM. Ultrasonic bone revealed bone induction locally at 2 weeks, while fresh bone didn’t induce bone and cartilage until 4 weeks. The new combination technique of ultrasonic irradiation and AEW will contribute to improve the surface area and the 3D-structure of the dense bone and should promote bone induction in the initial stage.