In Mt. O-akan and its adjacent areas, 220 taxa of lichens are recognized as the results of taxonomic study of 950 specimens collected there. Most of them are common in other areas of Hokkaido and on various mountains especially of northern Japan. Japewia subaurifera and Ochrolechia androgyna are newly recorded for Japan and Anisomeridium nyssaegenum, Calicium trabinellum, Chaenotheca brunneola, Chaenothecopsis pusilla, Hypocenomyce friesii, Lecanora imshaugii, Lecidea brachyspora, Ochrolechia akagiensis, Pannaria conoplea, Parmeliella grisea, and Placynthiella uliginosa are new to Hokkaido. In addition, Cladonia norikurensis, Glossodium japonicum, Lethariella togashii, and Tuckermannopsis microphyllica have been known to be rare or endemic to Japan and are also found in the present area.