The field observations were performed to understand the characteristics of growth and nutrient uptake of Phragmites japonica on flood plain in a gravel river, in which the temporal variation of plant biomass, the content of nutrients of vegetation and the concentrations of nutrients in the groundwater were measured. The result of the field observations show that the growth of the vegetation was restricted by the groundwater level in the present observation site. The hydroponics experiment of the riparian vegetation was conducted to understand the nutrition uptake due to photosynthesis. The results of the experiment show that the nitrogen uptake of the vegetation was closely associated with the amount of respiration of the roots of the vegetation.