Wetland areas have characteristics of dynamic cycling of materials in relation to land and water. Although having great potential for providing unique natural environments, they are vulnurable to human land use activities and some places are in danger of being eliminated. This study had an objective of investigating vegetation changes in Ilwol reservoir to provide basic information for the preservation and ecological restoration of the wetland area. Wetland vegetation was investigated along with the site conditions which may affect the vegetation development. There were 10 vegetation types with various species composition. Humulus japonicus, Zizania latifolia, Phragmites japonica, Bidens frondosa, Typha orientalis, Scirpus tabernaemontari, Phragmites communis, Persicaria thunbergii were the major wetland plants found at the reservoir area. Precipitation and water level were the elements mostly affecting the distribution of the plants. Phragmites japonica was closest to the water front, followed by Zizania latifolia, Humulus japonicus and Bidens frondosa. Most plant zones were predominated by one or a few species.