A phytosociological vegetation survey was conducted in July to September 2011 in order to examine the vegetation community structure in Mt. Ohseo area. It was aimed to provide basic data for the effective vegetation conservation by analyzing the importance, species diversity and community similarity of the forest community in Mt. Ohseo for each layer, followed by the classification of the actual forest vegetation. According to the cluster analysis, the community type of Mt. Ohseo was classified into a total of 4 vegetation communities: Pinus densiflora community, Cornus controversa-Quercus serrata community, Miscanthus sinensis community, and Quercus mongolica community; the vegetation type 4 showed the lowest species diversity index of 0.5236, and vegetation type-2 showed the highest species diversity index of 0.6606. The community similarity between Quercus mongolica community and Pinus densiflora community showed the highest 0.679, and the community similarity between Quercus serrata community and Pinus densiflora community and between Quercus serrata community and Quercus mongolica community showed the levels of 0.5, respectively.