In this study the main purpose is to reduce non-point source pollution and improve water quality of Hoeya reservoir using constructed wetlands. As part of the efforts to improve water quality of the reservoir, cattail and reed-wetland cells were constructed in front of the reservoir to remove nitrogen(N) and phosphorus(P). Also, effects of hydraulic and seasonal variation on removal efficiencies of N and P were investigated. Total P and N removal efficiencies of the wetland system were approximately 20.7% and 42.7%, respectively. Removal efficiencies of N and P during the growth season (july to august) and blooming season of cattail and reed (september to october) were higher than other seasons. These results suggest that wetland system could be an effective alternative for control of non-point source pollutnat such as N and P of reservoir.