Deposition level of sulphur is high and hence the cumulative load of sulphur is also high in East Asia. Since sulphur deposited on ecosystems may be retained in soil and/or cycled in the soil-plant system, manifestation of its effect may be delayed (e.g. Mitchell and Likens 2011; Kobayashi et al. 2012). Moreover, several rivers/lakes for monitoring on inland aquatic environment in the East Asian countries showed pH-declining trend with SO4(2-) increasing trend (EANET 2011). Effect of sulphur deposition on terrestrial ecosystems is one of the important issues to be investigated in East Asia. The scientists from the community of Acid Deposition Monitoring Network in East Asia (EANET) investigate the dynamics of sulphur derived from atmospheric deposition in forest catchments in Niigata, Japan, Nakhon Ratchasima, Thailand, and Sabah and Sarawak, Malaysia. In order to determine sulphur dynamics in the forest ecosystems, analysis of sulphur isotopic ratio is applied for rainwater, soil water and stream water in addition to measurement of the fluxes. The data obtained in the project will explain the possible impacts of sulphur deposition on the forests. Since nitrogen deposition is also quite high in the region, its relation to acidification/eutrophication could also be discussed.