Purpose: The aim of this study was to compare the ability of bone formation on single and multi-rooted tooth resulting from the placement of xenograft with different sizes of particles after immediate implant placement procedure in extraction sockets. Materials and Methods: Eight adult dogs were used. The first and second mandibular premolars were removed and replaced immediately by implants. On the left side, large particles (0.6∼1.0 mm) of xenograft (Biocera) was placed in the extraction socket, while the corresponding premolar sites on the right side were filled with small particles (0.4∼0.6 mm) of xenograft. After installation of implants, the stability was measured . Dogs were euthanized after 8 weeks and implant stability on the left and right side was measured. Also, BA and BIC were measured. Results: There was no clear difference between bone particle size in implant stability, BA and also BIC. Conclusion: The implant stability observed in extraction sockets did not show the significant difference between large and small particles of xenograft. Also there was no clear difference in single and double-rooted tooth. But the bone particle of small size is recommended. (JOURNAL OF DENTAL IMPLANT RESEARCH 2012;31(2):54-60)