It is clarified that acid species have been transported from the Asian Continent to Yakushima Island, and the major species in the acid depositions is sulfuric acid on this Island. The concentration rations of SO42- to the sum of NO3- and SO42- in rime-ice and rainwater were over 90%, as well as the river waters. The forest can be related to the cause of high ion concentration of G1 mountain stream, because it was clarified that Cl- in mountain stream water only of the atmospheric origin was concentrated on the canopy in the cause of water circulation from the rainfall to the river water. Therefore, SO42- of the atmospheric origin may have been concentrated similarly according to this process and then become in high concentration in the mountain stream water. It was examined whether these acid species influenced the water quality formation of the mountain streams in the western part of Yakushima Island, and found that the contribution of the H+ in the acid deposition resulted in the unexpected relation between the HCO3- and SiO2 concentrations.