The purpose of this study was to investigate effects of the natural coral(NC)and the hydroxyapatite/calcium sulfate hemihydrate(HA/CS)on an early stages of wound healing in the rat periodontal fenestration defects. In this experiment, twelve male rats(Mean :520g in BW)aged 8 to 9 months were used. Experimental periodontal fenestration defects were surgically created with tapered fissure bur at the buccal surface of the left mandibular 1st,2nd molars. The buccal aspects of molar roots were carefully denuded of their periodontal ligament through a bony window created in the left mandibles of rats under general anesthesia. Each experimental periodontal fenestration defect was grafted with natural coral and HA/CS, randomly. An area without bone graft was assigned for negative control group. At 10,35 days, rats were serially sacrificed via intracardiac perfusion with 2.5%glutaraldehyde and specimens were processed with Hematoxylin-Eosin stain for light microscopic evaluation. The results of this study were as follows : 1.The defect areas were filled with dense connective tissues at 10 days in control group. But in the test(NC, HA/CS)groups, the connective tissues around graft materials were formed more loosely and the response of inflammation by graft materials itself was not found. 2.The defect areas were filled with new osteoid tissues and new cementum was not formed on the cut root surface at 35 days in the control group. 3.New osteoid tissue formation was more prominent at 35 days in control than test groups. 4.The NC and HA/CS particles were encapsulated by loose connective tissues at 10 days and by dense connective tissues at 35 days, respectively. 5.In the test groups, resorption of graft particles was not found through the experimental time. From the above results, natural coral and hydroxyapatite/calcium sulfate hemihydrate may be biocompatible and osteoconductive and have a weak adverse reaction to the periodontal tissues.