The flora of the studied basin in the upper Keum River was listed as 237taxa; 63families, 162genera, 212species, 22varieties and 3forms. Based on the list of the ecosystem disturbance plants by the Ministry of Environment, 4taxa were recorded in the studied basin : Paspalum distichum(Gramineae), Paspalum distichum var. indutum(Gramineae), Ambrosia artemisiifolia var. elatior(Compositae), Ambrosia trifida(Compositae). Naturalized plants was listed as 54taxa; 16families, 41genera, 51species, 3varieties and naturalization index was 22.8percent of 1/4 the vascular plants. Upper Keum River was dominant floristic : indicator species were Salix gracilistyla community, Phragmites japonica community, native plants were Morus alba community, Spiraea prunifolia for. simpliciflora community, planting plants were Populus euramericana community, naturalized plants were Solidago serotina community, Helianthus tuberosus community.