Bone formation on hydroxyapatite (HA) coating in the presence of gaps is important for clinical application. Pure Ti and hydroxyapatite coated by plasma sprayed samples were implanted in dog respectively. The implants were surrounded by gaps of 2 mm, and the follow-up period was 12 weeks. Histological examination and histomorphometry revealed that gaps could be bridged by bone provided the hydroxyapatite coating was applied, and that pure Ti implants were surrounded by fibrous tissue with no bone contact at all.