Synthetic bone graft materials have been used for the regeneration of periodontal tissue lost due to periodontal disease, but the limitations of these materials had prompted the use of composite grafts. Among those, a composite graft of calcium carbonate(CC) and calcium sulfate(CS) is one of those materials that has not been studied extensively. CC, which is extracted from a natural coral, is known to possess osteoconductive property. SC can play an adjunctive role in the regeneration of bone tissue, and has shown good resorbability and biocompatibility. This study was conducted in order to investigate the effects of CC and CS composite graft to the regeneration of bone in the intrabony defects of dogs. 3-wall intrabony defects ub size of $4mm{ imes}4mm{ imes}4mm$ were created in the alveolar bone in the premolar areas. Then those defects that were treated with root planning only were designated as control, while the experimental group 1 and 2 each received the CC and CS composite grafts in the ratio of 8 : 2 and 5 : 5 the animals were sacrificed after 8weeks and the specimens were histologically analyzed. The results were as follows ; 1. No inflammation or foreign body reaction were observed in all subjects. CS has not been seen due to complete resorption, and resorption pattern of CC was observed. 2. Significant differences(p<0.05) in new cementum formation were observed between control($1.42{pm}0.64mm$) and experimental groups(group 1 ; $2.53{pm}0.94mm$, group 2 ; $2.23{pm}0.96mm$) but the difference between the two experimental groups was not significant. 3. Significant differences(p<0.01) in new bone formation were observed between control($0.59{pm}0.55mm$) and experimental groups(group 1 ; $2.27{pm}0.61mm$, group 2 ; $2.05{pm}0.56mm$) but the difference between the two experimental groups was not significant. 4. The extent of apical epithelial migration has shown no significant difference between control($1.18{pm}1.24mm$) and experimental groups(group 1 ; $0.51{pm}0.54mm$, group 2 ; $0.73{pm}0.70mm$). 5. The extent of bone formation was generally limited to the extent of cementum formation for all groups, and significant correlation was found in the amount of bone formation and cementum formation in experimental group 1.(Co.=0.86, p<0.01) These results suggest that the composite graft of CC and CS is biocomplatible and effective in the new bone and new cementum formations. In the case of 3-wall intrabony defects of dogs, the composite ratio of 8 : 2 and 5 : 5 had shown no significant differences in the healing.