This study was carried out to investigate the flora of Jingangsan Mt. (Ganghwa-gun). The vascular plants identified during the 11 round field surveys were a to total of 560 taxa: 114 families, 336 genera, 495 species, 7 subspecies, 53 varieties, 4 forms and 1 hybrid. A high plant diversity were Poaceae (11.0%), Asteraceae (10.8%), Cyperaceae (8.8%), Rosaceae (4.6%) and Lamiaceae (4.3%) in regular order. The four taxa of Korean endemic plants such as Viola seoulensis Nakai, Salix koriyanagi Kimura ex Goerz, Hemerocallis hakuunensis Nakai and Polygonatum infundiflorum Y. S. Kim, B. U. Oh & C. G. Jang were collected. The vascular plants on the red list according to IUCN evaluation basis were found to be four taxa: Near Threatened (NT) species of Delphinium maackianum Regel, and Not Evaluate (NE) species of Mosla japonica (Benth. ex Oliv.) Maxim., Carex paxii Kük. and Polygonatum infundiflorum Y. S. Kim, B. U. Oh & C. G. Jang. The floristic regional indicator plants found in this area were 28 taxa comprising two taxa of degree Ⅳ, three taxa of degree Ⅲ, eight taxa of degree Ⅱ, and 15 taxa of degreeⅠ. In addition, the naturalized plants were identified as 44 taxa and the percentage of naturalized index (NI) was 7.9%, and Urbanization Index (UI) was 13.7%.