The osteogenic potential of autologous bone marrow derived mononuclear cells(MNCs) mixed with atelocollagen and hydroxy apatite when transplanted to bone defects was evaluated. 15 mm defect on radius were made in 27 NZW rabbits. The rabbits were divided into control, MATREX-B(atelocollagen and hydroxyl apatite mixture) and ASTEM-B(MATREX-B and MNCs mixture) groups as treatments. Each group was scheduled to be sacrificed at 3, 6 or 9 weeks after the operation and took an x-ray for radiological evaluation and tissue staining with Masson`s trichrome. At 9 weeks after the operation, ASTEM-B and MATREX-B treated group showed an excellent bone healing results. At 6 weeks after the operation, ASTEM-B treated group showed that most of the injected collagen gel formulation was converted to bone like tissue in the defect area. At 6 weeks after the operation, MATREX-B treated group showed an initial step in bone remodeling process. In case of control group, bone healing effect in defect area at 6 or 9 weeks after the operation showed a slight bone formation, but symptom of bone remodeling was not observed. In this research, atelocollagen gel formulation with autologous bone marrow derived mononuclear cells showed an accelerated bone healing using the rabbit model with critical bone defect.