Mass loss and changes of mineral nutrient during the decomposition of Typha angustata for 13 months from November in 1998 to December in 1999, were investigated in small watercourse in Boryeong, Chungnam Province, Korea. After 13 months, remaining mass of leaves, stems and rhizomes was 34.7%, 59.2%, 7.2%, respectively. The rate of weight loss of the rhizomes was significantly higher than those of the leaves and stems. The decay rate of leaves, stems and rhizomes was 1.06, 0.52, $2.63 yr^{-1}$, respectively Initial concentration of nutrients in leaves, stems and rhizomes was 11.5, 9.0, 14.5 mg/g for N, 0.30, 0.27, 0.47 mg/g for P, 20.7, 26.9, 26.6 mg/g for K, 14.50, 4.77, 3.25 mg/g for Ca, and 1.99, 1.32, 2.07 mg/g for Mg, respectively. Except for Ca, concentrations of nutrients in rhizomes were higher than those in stems and rhizomes. There was no immobilization period during the decomposition of each organ of T. angustata. In case of K, most are lost during the first 1 month. Phosphorus in decomposing leaves and stems lost 58% and 66%, respectively, of the initial P capital within 1 month. [Decay rate, Decomposition, Immobilization, Macrophytes, Nutrients, Typha angustata].