We have previously reported an inverse ceramic foam method aiming to improve mechanical strength of calcite foam that has interconnected porous structure. The modified foam was obtained by multiple Polyurethane coating. In previous study, calcium hydroxide (Ca(OH)2) slurry was poured into the foam. After drying, the foam was burnt out to remove polyurethane and to carbonate Ca(OH)2 under mixed O2-CO2 atmosphere. Ca(OH)2 was completely converted to calcite. Those calcite foams are the useful precursors for the preparation of the three-dimensional (3D) interconnected porous carbonate apatite (CO 3AP) foam. Therefore, we investigated the hydrothermal treatment of calcite foam to CO3AP foam in phosphate solution. The results indicated that the conversion ratio depends on the degree of porosity of calcite precursor and calcite foam was completely transformed to CO3Ap foam at 100°C for 14 days. The CO3AP foam showed the increase in the compressive strength compared to conventional foam. So, it is concluded that CO3Ap foam fabricated in this study could be a good candidate for the bone replacement material in clinical application.