This study was carried out to investigate the flora of Mt. Byeollipsan (Ganghwa-gun). The vascular plants from 13 field surveys were revealed to total of 574 taxa; 116 families, 355 genera, 505 species, 8 subspecies, 52 varieties, 7 forms and 2 hybrids. A high plant diversity were Asteraceae (12.3%), Poaceae (10.6%), Cyperaceae (6.1%), Fabaceae (4.5%) and Rosaceae (4.2%) in regular order. The seven taxa of Korean endemic plants such as Clematis brachyura, Viola seoulensis, Populus × tomentiglandulosa, Salix koriyanagi, Ajuga multiflora f. rosea, Hemerocallis hakuunensis and Polygonatum infundiflorum were collected. The red data of vascular plants according to IUCN valuation basis were examined five taxa; Least Concern (LC) species of both Phacelurus latifolius and Belamcanda chinensis, Not Evaluate (NE) species of Lithospermum arvense, Scorzonera austriaca ssp. glabra and Polygonatum infundiflorum. The floristic regional indicator plants found in this area were 34 taxa comprising one taxa of degree IV, six taxa of degree III, 11 taxa of degree II, and 16 taxa of degree I. In addition, the naturalized plants were identified as 46 taxa and the percent of naturalized index (NI) was 8.0%, Urbanization Index (UI) was 14.3%, respectively.