To evaluate the possibility of the newly developed highly porous glass ceramics as a space-filler in the cavitary bone defect, we made the opening sized 1 × 0.5 cm on the medial aspect of the right proximal tibia of nine rabbits. We impacted the highly porous glass ceramics firmly to the medullary cavity of rabbit tibia through the opening. Each three were sacrificed at 4th, 8th, and 12th week and analyze in vivo reaction of the glass ceramics in rabbit tibia with radiological and histological methods. On radiological examination, radiolucent line was seen around impacted glass ceramics at 4th week, but this radiolucent line was obliterated gradually to 12th week. On histological examination, new bone formation with osteoblast was appeared at 4th week without foreign body reactions. At 8th week, newly formed bone infiltrated into the porous space between glass ceramics particles was noticed, and the surface of glass ceramics was tightly bound by newly formed bone with osteoblastic rim and mature bone, At 12th week, the amount of newly formed mature bone increased, though there was on evidence of resorption of glass ceramics particle. So, we suggest that the highly porous glass ceramics is one of the possible artificial bone graft substitutes, especially as a space-filler.