Bone or bone substitute has been widely used for the reconstruction of bony defect developed by trauma, infecton, cyst, tumor, congenital abnormality, etc. Owing to its variety in quality and quantity, the use of alloplasts is increased rapidly. Among the various graft materials, HA has been studied and applied in clinic most exensively. When HA applied to bony defect, it is considered to help the bone healing by osteoconduction but tends to be encapsulated with fibrous tissue and floated in the applied area by the lack of consolidation. Bioglass is considered as a subsitute which can cover such weak point of HA. Bone defect were artificially prepared in the calvaria of the rats followed by grafts of HA and bioglass into defects. Sequential sacrifice was peformed at the 3rd, 7th, 14th and 28th day of experiment. The staining of the obtained specimen was performed with H&E, MT, immunohistochemical stain and then histological examinaions were carried out under the light and scanning electron microscope. 1. In the features of H&E stain, infiltration of chronic inflammatory cell were present in all group at the 3rd and 7th day of experiment with decrease at the 14th day in bioglass group. The infiltration of inflammatory cells was more active in control and HA group whereas the formation of granulation tissue was more active in bioglass group was larger and more irregular than in HA group. 2. The features of MT stain showed new bone formation from the 7th day in all groups and the evidence of advanced calcification was observed at the 28th day. 3. In the features of immunohistochemical stain, bioglass group showed more PCNA positive response in the osteoblasts at the site of new bone formation and the lower activity of undifferentiated mesenchymal cells than HA group. 4. In scanning electron microscopic features, fibrous tissue formation and osteoid attached to HA was observed in the HA group after the 7th day. In bioglass group, osteoid formation was observed between the absorbed bioglass. Generally in HA group, bone formation progressed with characteristic of the fibrous and osteoid tissue mainly attached to the surface and the high activity of undifferented mesenchymal cells was seen at the graft site. In bioglass group, osteoid tissue formation was seen between the irregulary absorbed bioglass and the increased PCNA positive response was observed in the osteoblast at the new bone formation site.