SUMMARY. “Application of the Jouyban-Acree model for Estimating the Solubility of Naproxen in Ethanol + Water Cosolvent Mixtures”. In this work the validity of a trained version of the Jouyban-Acree (J-A) model was evaluated to predict the solubility of naproxen in ethanol + water cosolvent mixtures. The usefulness of the solubility log-linear equation proposed by Yalkowsky and Roseman (Y-R) was also evaluated for the same drug in this cosolvent system. The solubility estimation was studied as a function of temperature and cosolvent composition. The J-A and Y-R models require only the experimental solubility values in the pure solvents at all the temperatures evaluated. The calculated values by using both models were similar between them but they notoriously deviated from experimental values presented in the literature.