This study was carried out to investigate the flora of Mt. Biseul. The vascular plants collected 10 times(from May 2006 to October 2007) were identified as 468 taxa in total, including 89 families, 302 genera, 397 species, 1 subspecies, 59 varieties and 11 forms. Korean endemic plants of this area were identified as 17 taxa including Thalictrum uchiyamai, Coreanomecon hylomeconoides, Lonicera subsessilis, etc.; the Ministry of Environment-designated plants, which should be protected by the wildlife protection law, were identified as one taxon including Aconitum austrokoreense; the Office of Forestry-designated rare & endangered plants were identified as 6 taxa including Viola albida, Lloydia triflora, Streptopus ovalis, etc.; the naturalized plants were identified as 34 taxa, and their naturalization ratio and urban index were found to be 7.3%, and 12.2% respectively. This study newly identified about 160 taxa of the plants, among which 17 taxa were newly added to the list of naturalized plants, such as Phytolacca americana, Dicentra spectabilis, Lepidium apetalum, Medicago lupulina, Euphorbia supina, Ambrosia artemisiifolia, Cosmos bipinnatus, Crassocephalum crepidioides, Galinsoga ciliata, Rudbeckia bicolor, Sonchus oleraceus, Tagetes minuta, Taraxacum officinale, Chloris virgata, Festuca arundinacea, Lolium perenne, Tradescantia reflexa, etc. There existed many kinds of plants resources having conservational value like Aconitum austrokoreense etc. in this area, but there remains a fear of nature destruction's acceleration due to indiscriminate human development and access of a lot of visitors, so it is judged that there should be a management plan, such as a limit on the number of visitors or rest-year-system for restoration of nature.