Apatite ceramics composed of synthetic hydroxyapatite, Ca10(PO4)6(OH)2 were implanted in mandibles of adults dogs. The histological observations indicated that the apatite ceramic was closely contacted with newly formed bone tissue without any rejection phenomenon up to 2 weeks. An electron micrograph of non-decalcified ultra-thin section at 8 weeks showed that the apatite ceramic was directly bonded to newly formed bone and the mineralized bone tissue was grown into the micro pores of the ceramics independent on the pore size. It seemed that the outer surface of the apatite was exchanged by bone tissue. From these results it was considered that the apatite ceramic was a successful implant material in dental and surgical fields.