Carbonate apatite (CO3 Ap), an inorganic component of human bone, has been clinically applied as an artificial bone substitute. In this study, the effects of the CO3 content in CO3 Ap on the replacement by new bone were studied by fabricating CO3 Ap granules containing 0.9-8.3 wt% of CO3 . The dissolution rate of CO3 Ap in a weak acidic solution, mimicking the Howship's lacunae, was rapid for the CO3 Ap granules containing a larger amount of CO3 . Histological analyses demonstrated the rapid resorption in CO3 Ap and replacement by natural bone tissue when the CO3 content was increased. Therefore, the CO3 content in CO3 Ap is a key factor that influences the replacement of the bone tissue.