This study is to investigate the degree of river naturality according to the river morphology and the flora on the Sosa River at three regions during four seasons. Number of flexion was three at upper region and those of middle and low regions were one. Transversal and longitudinal sandbars were absent. Materials of river shore and river levee at low channel width were state of nature without protecting materials at upper region and those of middle and low regions were many artificial levee. The flora on the Sosa River was a total of 65 taxa, including 25 families, 58 species, and 7 varieties. Naturalized species were 8 families and 22 species. The construction of the reservoir has caused the quantitative collapse of the river area and cause the qualitative reduction of the riparian.