The approach tested in this work consists in adapting the Pitzer model, initially designed for aqueous electrolyte solutions, to the case of solutions with a mixed solvent. This modified model was applied to KCl, LiCl, CsCl, RbCl, HCl, NaCl and NaBr in methanol-water mixtures at 25 degrees C. The results show that the calculated mean activity coefficients of the electrolytes studied are in good agreement with experimental values obtained from the literature.