We investigated chemistry of soil water at 10 cm depth, together with bulk precipitation, throughfall and stream water at a deciduous broadleaf forest on Mt. Sentsu, Shimane, the headstream of Hiikawa River. Vegetation in valley bench and lower part of slope was consisted of plant species which are characteristic of riparian forests. Increases of dissolved organic carbon （DOC）, <NO_3>^-, <NH_4>^+, Mg^<2+> and Ca^<2+> concentrations were observed in the soil water compared to bulk precipitation and throughfall. Mg^<2+> and Ca^<2+> concentrations were positively correlated to <NO_3>^-, probably due to ion exchange at the surface of soil particles accompanied with nitrification. <NO_3>^-, Mg^<2+> and Ca^<2+> concentrations were higher in the valley bench than in the upper slope, indicating active nitrification in the valley bench. Compared to the surface soil water, DOC, <NO_3>^-, <NH_4>^+, and Ca^<2+> concentrations decreased remarkably in the stream water, suggesting presence of removal processes of DOC and these ions in deeper soils and groundwater. Presumably plant uptake of nutrients and denitrification may strongly remove DOC and these ions in deeper soils in the valley bench. Results from our study indicate that the process in riparian forests would contribute to prevent nitrogen leaching to stream and to control water quality in rivers.