In the Mekong River basin, Lao PDR, relocation of villages and governmental restriction to the slash and burn agriculture has been in operation since 1980s. These social and political backgrounds could possibly alter basin-wide land use and land cover status and cause adverse hydrological impacts. However, no analysis was conducted based on measurement data to reveal the land use change and relate it to watershed-scale hydrological responses. Thus, this study aims at revealing the hydrological impacts of land use changes in mountainous sub-watersheds of the Mekong River basin by analyzing rainfall-runoff response and trends of monthly rainfall and streamflow.