Precipitation variation always has an effect on the river streamflow. The change in discharge greatly impacts aquatic habitats, environmental amenities, recreational opportunities, irrigated agriculture production, hydropower production, and other industrial water uses. Therefore, studying the streamflow trends is important guidance for stakeholders and decision-makers to make a long-term and suitable management strategy. The aim of this study was to analyze the trend of monthly streamflow in the Prek Thnot River of the Lower Mekong Basin. Daily streamflow data of four stations recorded in the Prek Thnot River between 1997 and 2011 were assessed using the Mann-Kendall (MK) test and Sen’s slope estimator to evaluate the statistical characteristics of streamflow distributions for the trend analysis. The result highlight that these statistics of the streamflow were observed that monthly flow begins to increase from May to October and rapidly decreases from November to April. The rainy season of streamflow is higher than the dry season. From the statistical analysis in the Prek Thnot River Basin, the streamflow trend slightly decreased from 1997 to 2011. Furthermore, the annual peak and low flows occurred in 2001 and 2005, approximately 83 and 11.5 m3/s, respectively. Results Mann-Kendall test of monthly streamflow were revealed only at the significant level of 0.1 in May for Tasal Dam, while the slope magnitude estimated by Sen's Slope estimator is about 0.45. The slope was positive during the early rainy season, indicating that the monthly streamflow quantity increased during this period. The tests also revealed that most months were no trend evidence and had a sign fluctuation of streamflow throughout the period.