Description: Publication date: Available online 19 February 2018 Source: Water Science Author(s): Raksmey Ang, Chantha Oeurng The study objective of this work is to test the applicability of the Soil and Water Assessment Tool (SWAT) model to simulate the streamflow through calibration and validation for both daily and monthly basis in the Stung Pursat River catchment, an ungauged sub-catchment of Tonle Sap Basin in Cambodia. In order to achieve the objective of the study, SWAT model was set up with study period of 10 years (2001–2010). Additionally, ArcSWAT2012 and ArcGIS10.2.2 combined with Sequential Uncertainty Fitting-2 (SUFI-2) algorithms were used to conduct uncertainty analysis, calibration and validation of the SWAT model using daily observed streamflow data at the catchment outlet. Daily simulation produced the results with Nash-Sutcliffe Simulation Efficiency (NSE) of 0.38, Percent Bias (PBIAS) of +5.1% and Root Mean square error-observation standard deviation Ratio (RSR) of 0.79 in calibration period, and with NSE of −6.61, PBIAS of −78.38% and RSR of 2.67 in validation period. The streamflow results of monthly time series were improved and acceptable with NSE of 0.60 while decrease the value of PBIAS and RSR to 1.14, and 0.63 respectively. The SWAT model should be used to simulate monthly streamflow in such an ungauged catchment like the Stung Pursat catchment due to data scarcity and uncertainty.