The pH determining factors of the streamwaters in various types of forest basins were globally examined based on a simple CO2-HCO3- equilibrium model which has been effective in understanding the buffering and in particular the hydrochemical systems of the Japanese temperate forest basins. The comparative analysis was applied to the forest basins in Eastern North America, Northern Europe, Mediterranean Europe, the south east Asian region including tropical rain forests, and the warm and cool temperate area of Japan. The results prove that the concentration of bicarbonate, which is treated as an index of the chemical weathering rate, controls the pH value remarkably more than the p(CO2), which is an index representing the biological activities in forest soils. The chemical weathering level that is indicated in the bicarbonate concentration of each forest basin corresponded reasonably well to the geological classification and soil generation characteristics of each forest basin.