The purpose of this study was to investigate the immunohistochemical and the ultrastructural features of the implant circumference epithelium of the beagle dog using various types of antibodies. The peri-implant epithelium was at an acute-angle from the gingival epithelium and was arranged in parallel to the implant surface. With immunohistochemical staining, the peri-implant epithelium was strongly positive for KL-1, and weakly positive for CK4, CK8 and CK19. These positive reactions for keratins and also for PCNA and BM-1 were similar to those seen in the oral mucosa. In the peri-implant epithelium, a plentitude of microvilli were observed at the periphery of cells at the implant sites, and bacteria were observed between the implant and the peri-implant epithelium without the formation of half desmosomes. There were many lipid-like vacuoles or lysosome-like granules. The intercellular space was wider than the junctional epithelium, and random migrations of large numbers of neutrophils could be seen. Taken together, the peri-implant epithelium is similar to that seen in the oral mucosa, and it is structurally different from the junctional epithelium.