This paper focuses on calibration and validation of a hydrologic model of the Rio Conchos Basin, a main Mexican tributary of the binational Rio Grande Basin. The Rio Conchos provides approximately 55% of the water deliveries to the United States under the 1944 water treaty signed between both countries. The hydrologic modeling has been developed using the one-dimensional, two-layer soil moisture accounting scheme embedded in the Water Evaluation and Planning (WEAP) model. A 10-year period was used to calibrate the model, which was achieved by a trial-and-error method for the adjustment of the model parameters. The results show a Nash-Sutcliffe coefficient of 0.84 at Ojinaga station (mouth of the basin) and 0.81 at La Boquilla, indicating good model performance. In general the model predicts well the monthly, annual, and maximum flows; but there are significant differences between the model values and undeveloped (naturalized) flows for low flow periods, especially at La Boquilla station. For model validation, a special period of 10 years was used, corresponding to drought conditions in the basin. Results show a Nash-Sutcliffe coefficient of 0.88 at Ojinaga station, with error in annual volume less than 1% on average.