A floristic study on the vascular plants from Mt. Seounsan region, which ranges from Seoun-myeon, Anseong-si, Gyeonggi-do to Baekgok-myeon, Jincheon-gun, Chungcheongbuk-do, was conducted 9 times in total, from April 2014 to October 2015. Based on the voucher specimens, it was revealed that the vascular plants in this region comprised 501 taxa: 97 families, 306 genera, 439 species, 5 subspecies, 51 varieties, and 6 forma. Among these plants, 185 taxa were recorded for the first time from this region. 8 Korean endemic species including Asarum patens (K.Yamaki) B.U.Oh, Scutellaria insignis Nakai, and Weigela subsessilis (Nakai) L.H.Bailey were found in this region. 5 taxa of rare plants designated by the Korea Forest Service, including Iris ruthenica KerGawl., Leontopodium leontopodioides (Willd.) Beauverd, and Tricyrtis macropoda Miq., were also found. 11 taxa of floristic regional indicator plants in the 3rd to the 5th degrees were identified. In addition, 46 taxa of naturalized plants were recorded, and 2 taxa of ecosystem disturbance plants, which were Ambrosia trifida L. and Aster pilosus Willd., also found.