The impacts of climate change on hydrological processes in Stung Sen Catchment, the largest tributary contributing to Tonle Sap Great Lake in Cambodia, were assessed using the SWAT (Soil and Water Assessment Tool) hydrological model. The model was calibrated and validated using daily streamflow records. The calibration and validation results indicated that the SWAT model was able to simulate the streamflow reasonably, with R2, NSE, PBIAS, and RSR equal to 0.74, 0.71, -17.28% and 0.54 for the calibrated period, respectively. For the validation period, the values R2 = 0.69, NSE = 0.67, PBIAS = -18.35%, and RSR = 0.58 suggest that there was a good agreement between the simulated and observed streamflow during this period. The hydrological response to climate change was simulated based on the calibrated model. The climate change scenarios were built by using a downscaling method (delta change method) based on the outputs of three General Circulation Models (GCMs): GFDL-CM3, IPSL- CM5A-MR and HadGEM2-CC using Coupled Model Intercomparison Project Phase 5 (CMIP5) driven by RCP 4.5 and RCP 8.5 emission scenarios for two-time horizons (2050s and 2090s). Under the climate change impacts, the simulated results exhibit that the annual streamflow is projected to decrease in the 2050s by 3% to 14% and expected to change in the 2090s from 8% to 17%. In addition, for 2050s projection, climate change caused to change in all water balance components, including changed in actual evapotranspiration from -0.4% to 0.7%, surface runoff by -8% to 35.9% and decreased in groundwater discharge from 0.3% to 8.7%. Furthermore, climate variability will also lead to decrease in lateral flow from 7.5% to 24.4%, while the water percolation is decreased from 0.3% to 8% and the water yield is decreased by 2.2% to 13.5%. Additionally, climate change caused to increased in potential evapotranspiration range from 3.7% to 7.2% for the projection in 2050s. Moreover, in the 2090s, the results also indicated that the climate change in the study area is predicted to increase surface runoff from 66.6% to 83.5% , the actual evapotranspiration from 1.3% to 1.4% and the potential evapotranspiration from 7.6% to 14.7%. Otherwise, the projection result in the 2090s is also predicted to change in groundwater discharge from -17.6% to 5.2%, lateral flow from -1.8% to 5%, water yield from -5.9% to 5.9% and the water percolation gonna vary from -2% to 5.5%.The results obtained in this study are expected to enhance the understanding of the impact of climate change on hydrological components through investigating the historical and future impacts of climate change and to provide information that decision-makers need in integrated river basin management as well as the development of adaptation and mitigation strategies regarding climate changes condition.