Rapid population growth and industrialization have increased water stress for Kedah River basin. Kedah state is popularly known as the rice bowl of Malaysia. A study on the future water resource availability is important to ensure the sustainability of the basin development. A water allocation model was set up using Water Evaluation and Planning (WEAP) software. The model was calibrated using data from year 2002 to 2016, taking into consideration system demand, system losses, return flow, reservoirs inflow, and outflow. Validation based on the residual flow derived from the basin water balance study shows good agreement of historical water levels at the reservoirs. Using the projected future climate and water demand, model simulations were performed up to year 2060. The findings shows that wet and dry extremities attributed to climate change effect are likely to impact the basin significantly. Unmet water demand increases from year to year leading to potential water supply deficit in the basin. Kedah River basin is thus in pressing need for a comprehensive water resource study and planning in order to be well-prepared for these future scenarios.