Autograft is frequently used to restore anatomic morphology and functional properties in bone defects. Disadvantages of the autograft are related to donor site morbidity and include the risk of wound infection, increased blood loss, and additional postoperative discomfort. Allograft and xenograft, which are currently employed as the most common alternative to autografts, encounter the complications. such as fracture, resorption, and nonunion secondary to immunologic rejection. Hydroxyapatite(HAp), a calcium phosphate ceramic, is a well known biocompatible artificial bone substitute without induction of systemic toxic and foreign body reactions. Bone conduction is usually occurred by the implanted HAp. Biodegradation of HAp is poor and the bone formation around HAp is slow and about more than 70% of the natural apatite in bone is composed of carbonate apatite that has carbonic radical(CO₃) instead of hydroxyl radical(OH-) or Phosphate radical(PO4 ) of HAp. Carbonate apatite ahs been known as that the physicochemical properties are similar of the natural bony apatite. In vivo experiment, carbonate apatite demonstrates non-toxic reactions. In this study, the compostite consisted of carbonate apatite and type I collagen, which is the bony structural protein, was implanted in rabbit tibiae to evaluate possibility as an artificial bone substitute. Biodegradation rate of the composite, the rate and qiantity of the regenerative cortical and cancellous bone formation were investigated radiologically and histopathologically. HAp and the carbonate apatite coilagen composite(Ap-C) were applied in the dissected rabbit tibiae(7-8mm), and fixed by external fixators. Postoperative roentgenograms were taken 2, 4, 6, and 8 weeks after implantations. For histological ohservations, the rabbits were sacrificed and the specimens were obtained 2, 4, 6, and 8 weeks after operation. Radiological Lane scores of Ap-C were 1.16±0.92, 2.16±0.98, 3.33± 0.82, and 3.67±0.51 in 2. 4, 6 and weeks after operation, while the Lane score of HAp were 0.53±0.84, 0.83±0.75, 1.67±0.81, and 2.83±0.98 respectively. Ap-C demonstrated the faster degradation and more bone formation then HAp. Though physicochemical properties of carbonate apatite is similar to those of HAp, the carbonate apatite and type I collagen composite(Ap-C) revealed rather faster degradation and bone formation than HAp in both radiological and histological investigations.