To evaluate the water purification capacity of 4 emergent macrophytes in 4 tributaries of Mankyung River, nitrate reductase activity (NRA) and nutrient removal capacity were determined. Higher NRA occurred in emergent macrophytes such as Persicaria thunbergii and Oenanthe iavanica with 7.8 and 5.4 ${mu}$moi NO$_2$ g$^{-1}$d.wt. h$^{-1}$. respectively. The nitrogen removal capacity of emergent macrophytes displaying higher NRA fell within the range of 0.85 to 1.95 mg g$^{-1}$d.wt. day$^{-1}$ and was higher in the order Phragmites communis > Persicaria thunbergii > Oenanthe iavanica > Zizania latifolia. The phosphorus removal capacity was within the range of 0.07 to 0.12 mg g$^{-1}$d.wt. day$^{-1}$ and was higher in the order Phragmites communis > Oenanthe iavanica > Persicaria thunbergii > Zizania latifolia. In all the domestic, industrial and agricultural wastewaters, Phragmites communis showed the highest nitrogen and phosphorus removal capacity; 1.36 and 0.0088 mg g$^{-1}$d.wt. day$^{-1}$ respectively. Among the 4 macrophytes. Phragmites communis was the most suitable species for water purification in 4 tributaries of Mankyung River.