This study aims to evaluate the performance of our recently developed microspheres of hydroxyapatite/reconstituted collagen as a bone grafting material. The microspheres were fabricated into a circular disc and implanted in a pre-drilled hole in a rat's calvaria. The bone tissue had regenerated and grown into the disc bone graft 4 weeks following implantation. After 16 weeks of implantation, the regenerated bone had integrated with the remaining material and made close contact with it. The disc had been completely absorbed with almost no visible bone graft left after 24 weeks of implantation. In contrast, a hydroxyapatite disc still remained intact on the 24th week after implantation. These results suggested that the hydroxyapatite/reconstituted collagen microsphere can be used as an excellent bone grafting material.