The forecast of the polluting effects over a hydric basin is a constant need for the official environmental managers and for the people responsible for the decisions in this subject. Therefore, mathematical models that allow forecast damages or improvements in the river basin water quality are important tools for this purpose. Qual2E appears as one of these tools, of free access, and suitable for one-dimensional well-mixed rivers with constant flow. The objective of this work is to apply the Qual2E model to Corumbataí River, located in São Paulo State, in order to obtain a representative curve of the river water quality. The method suggested by the model request the division of the river in reaches with similar hydric features and a subdivision of these reaches in computational elements (CEs) with the same extension. The flow data, depth, DO (Dissolved Oxygen) concentration, BOD (Biochemical Oxygen Demand), temperature, load and location of pollution sources were obtained from a joint project between CETESB and USP, that resulted in a database for the water quality of the basin. This geo-referenced database was used both for the initial conditions to the model, as for the determination of a reference curve with the real field data, for comparison with the calculated curve of the model. The reaction coefficients - resulting from the interaction between DO and BOD - are the constants of the differential equations system solved by the model, were estimated through trial and error, until the agreement with the observed data. The calibration was efficient to reproduce the field data, through the validation for another group of data. A sensitivity analysis was executed for the parameters k1, k2, k3 and k4 and the calculated curve seemed to be more sensible to the BOD decaying coefficient. The limitations inherent to the model, the data collecting and the statistical treatment of the available data did not allow a better agreement between the calculated and the observed curves.