The composition changes of litters were investigated to figure out the effects of the decomposition of Humulus japonicus on nutrient circulation and decomposition process in the riverine wetlands: Tan stream and Amsa-dong. Litterbags (mesh size 1 mm and 5 mm) were installed to monitor mass and nutrient changes of 5 types of litters: H. japanicus only, Miscanthus sacchariflarus only, Phragmites communis only, mixed litters including H. japonicus, and mixed litters without H. japonicus for 7 months. It was shown that k (decay rate) of the H. japanicus ($2.68{sim}3.12$) was higher than that of M. sacchariflorus ($1.83{sim}2.16$) and P. communis ($0.02{sim}1.18$). The mass and organic remainings of the mixed litters including H. japonicus at Tan stream were $47.0{sim}55.1%;and;47.0{sim}54.9%$ and those of the litterbags without H. japanicus were $49.2{sim}65.4%;and;47.1{sim}57.5%$, respectively. This result indicated that the nutrient circulation was faster at H. japanicus community than others. Ca, Na, Mg, K, P, C, N and H contents reduced to around $40{sim}80%$ of original. However, Na concentration increased up to $407{sim}584%$ at 100 days and decreased to $248{sim}498%$ at the end of the experiment. Decomposition rates were similar between 1 mm and 5mm mesh size litterbags and this implies that plant litters in studied areas decomposed mainly by microbes rather than small animals. This study revealed that the fast growth of H. japonicus was resulted from fast decomposition in part: positive feedback of nutrient cycling.