Mass loss and changes of mineral nutrients during decomposition of Phragmites communis for 13 months from November 1998 to December 1999, were investigated at the fringe of stream at Boryeong, Chungnam Province in Korea. Plant materials, which were collected in November 1998. were divided into leaves, culms and rhizomes. Litterbags, 15${ imes}$15 cm, were made of nylon mesh with 2-mm$^2$ holes. At 13 months after installation, remaining mass of leaves, culms and rhizomes was 29.0%, 57.4%, 20.6%, respectively. Mass loss rate of the culms was significantly lower than those of the leaves and rhizomes. The decay rate of leaves, culms and rhizomes was 1.21. 0.42 and 1.48 per year, respectively. Initial concentration of N, P, K, Ca and Mg of leaves. culms and rhizomes was 22.5, 9.0, 15.5 mg/g for N, 0.34. 0.10, 0.33 mg/g for P, 15.0, 12.5. 12.3 mg/g for K, 2.84. 0.80, 0.03 mg/g for Ca. 1.94. 0.97, 0.40 mg/g for Mg, respectively. Concentrations of nutrients were higher in leaves than in culms and rhizomes. Except for N and Mg in rhizomes, there was no immobilization period during the decomposition. In the case of remaining K and Ca, most are lost during the first 3 months. Without any suitable method for removal of dead part, eutrophication of freshwater may be accelerated by dead macrophytes.