Climate and land use are two major factors that influence stream flow, especially in developing countries. This paper assesses potential changes to stream flow by considering future climate and land use in the Nam Xong watershed. The logistic regression method was applied to predict future land use in the study area. The predicted major change to land use was the conversion of wood and shrub land to agricultural land in the middle part of the Nam Xong watershed. The conversion to agricultural land, including tree plantations, is expected to increase in the future. Yet protecting forest areas and limiting deforestation is local policy. A hydrological model was applied to estimate daily stream flow, 222 m3/s in the wet season and 32 m3/s in the dry season, for the entire Nam Xong watershed. The scenario comparison showed that stream flow will decrease due to climate and land use changes over the next 20 years, especially in the middle part of the Nam Xong watershed where water is transferred to the Nam Ngum Reservoir. Here, stream flow will decrease by 11.7–12.2%; the overall figure for the watershed is 0.7–1.9%. Our results indicate that water management in the middle part of the Nam Xong watershed should be carefully considered.