The purpose of this study was to assess and compare the osseous responses to implanted particles of porous synthetic HA(Interpore 200(R), Interpore International, U.S.A.), resorbable natural bovine derived HA(Bio-oss(R), Gestlich Pharma, Switzerland) and calcium carbonate(Biocoral 450(R), Inoteb, France) in bone defects. Four calvarial defects of 2.5mm diameter were created in each of 16 Sprague-Dawley rats. The experimental materials were subsequently implanted in three defects, leaving the fourth defect for control purpose. Four animals were each sacrificed at 3 days, 1week, 2weeks and 4 weeks after surgery. The tissue response was evaluated under light microscope. Overall, histologic responses showed that all the particles were well tolerated and caused no aberrent tissue responses. There were difference in the amount of newly formed bone at the experimental sites and control site. There was more new bone formation associated with calcium carbonate site. In addition, the calcium carbonate site displayed multinucleated giant cells surrounding calcium carbonate particles after the 1st week, and osteoid tissue within the particle after the 2nd week. After 4 weeks, calcium carbonate particles were resorbed and replaced with new bone. The healing of the natural bovine derived HA site was similar to that of porous synthetic HA, except that new bone growth between the two particles have progressed more in the former site after the 2nd week. In the natural bovine derived HA site, the particle was surrounded by newly formed bone after the 4th week. After 4 weeks, the control site showed more mature bone than other sites. In conclusion, the grafted sites were better in new bone formation than non-grafted sites. In particular the calcium carbonate site showed the ability of osteoinduction and natural bovine derived HA showed osteoconduction in rat calvarial defects. This suggest that calcium carbonate and natural bovine derived HA could enhance the regenerative potential in periodontal defects.