This study aimed to better understand the hydrological response of the land use and land
cover change in the upper Mekong River basin located in LaoPDR. Under limited hydrological
and meteorological data availability, annual runoff ratio estimated for five sub-watersheds for the
period since the middle of 1980s showed increases by more than 10 points in Nam Khan and
Nam Suong watersheds, where a drastic change in the land use and land cover was found. This is
likely due to the introduction of the National Land Allocation policy and the relocation of
villages to the lowland areas. On the other hand, none to slight changes in land use were found
for Nam Lik and Nam Ngum watersheds, which correspond to relatively constant or even
decreasing runoff ratios. The seasonal Kendall test showed increasing trends of areal rainfall in
May for four watersheds, which support alleged early onset of the wet season. Increasing trends
of Streamflow in July is partly due to the increased rainfall in May, but the streamflow trend was
significant for watersheds where drastic land use change occurred in the 1990s.