Purpose: When autologous bone grafts are used, we needed surgical invasion to donor sites and autografts are limited amounts. Then, tissue engineered bone using bone marrow mesenchymal stem cells (MSCs) may supersede the need of such procedures. It is desirable that scaffold is biodegradable and replaced by new bone. The aim of this study is to observe osteogenic potential of biodegradable composite scaffold consisting of β-TCP and collagen sponge using 3D cultured MSCs in vivo. Methods: The β-TCP was used as the granular porous ceramic. Granule size was 0.5 to 1.0mm. A 1% atelo-collagen (type I and III) hydrochloride solution and β-TCP granule were mixed and homogenized. The β-TCP/collagen solution was poured into a mold and freeze-dried, followed by dehydrothermal cross-linkage. The bone marrow cells were harvested from the head of humerus of a beagle dog. The cell cultures were grown for 4 weeks to obtain plastic-adherent cell population including MSCs. The scaffold was soaked in cell suspension for 24 hours. They were implanted under the dorsum skin of dog, and were examined after 4,12 weeks. Results: At 4 weeks, the histological specimens showed that collagen sponge was degraded partially, and the most of β-TCP granules remained. Osteoblasts were founded surrounding of granules, and introduced a few newly bone formation. At 12 weeks, osteoblasts were decreased, but a lot of maturely formed bone was observed. The most of β-TCP granules were degraded, and replaced by new bone. This scaffold has potential for bone tissue engineering.