The distribution of native plants of Cheondeungsan Mountain (807 m, N 37°05'00“–37°05'30”, E 128°00'0“–128°02'0”) in Chungcheongbuk-do was determined and the major flora were identified. During field investigations carried out from May 2011 to October 2011, 87 families, 254 genera, and 369 taxonomic groups (327 species, 4 subspecies, 33 varieties, and 5 forms) were confirmed, and the distribution of 219 taxonomic groups was discovered for the first time. The distribution of four endemic plants of Korea, including Ajuga spectabilis Nakai and Salvia chanryoenica Nakai, and that of Penthorum chinense Pursh, a Grade V specific plant species, was found. There were 20 taxa of naturalized plants at Cheondeungsan; the growth and development of plants that are harmful to the ecosystem, such as Ambrosia artemisiifolia L., Ambrosia trifida L., Eupatorium rugosum Houtt., and Aster pilosus Willd., was observed around the forest paths and lowlands.