Negative impacts of hydropower dams on natural flow by creating fluctuations in daily high and low flow periods to meet electricity demands have been paid much attention recently. This issue should be thoroughly considered to ensure sustainable hydropwer development.  The objective of this study is to assess the impacts of dam construction on flow regimes and local livelihoods in this area. The study consists of two components: (i) Field survey including interviews and group discussions at different levels, and (ii) Flow alteration assessment. The field survey was then carried out to assess the impacts of dam construction on flow regimes and local livelihoods as well as to find the gaps between laws on water resources and its implementation. Then, the flow regime changes in the study area were assessed by applying the Indicator of Hydrologic Alteration (IHA) and Range of Variability Approach (RVA) methods to the historical data of streamflow before and after dam operation. The results from Key Informant interviews show that there are poor co-ordination and co-operation among administrative entities (province, district, commune), and between sub-sectors; unclear responsibilities in water resources management among departments as well as lack of human resources for water resources management at all levels. The results from household interviews and group discussions indicate that local people have felt differing livelihoods impacts from hydropower projects. Finally, the results from flow alteration assessment shows that flow regimes have been altered after dam operation, particularly during the low and high pulses. As a recommendation, it is suggested that the Law on Water Resources as well as the relevant sub-documents are reviewed and revised so that the roles and functions of actors become clearer. It also suggests that the trade-off between instream and offstream users/sectors should be considered in allocating water for better water resources management.