The thermodynamic dissociation constants of glycine and dl-alanine in 0, 20, 40, 60 and 80% (w/w) water-ethanol mixtures at 30degreesC and at a constant ionic strength I-s = 0.1 M KNO3 have been measured pli-metrically wAng Irving and Rossotti technique. pK(1) and pK(2) values in aqueous medium have-been found to agree well with previously reported ones. It is observed that the pK(1) of these acids increase regularly with the increase of ethanol contents in the mixtures while pK(2) values show show distinct minima ca. at 40% (w/w) ethanol content. The variation in pK values with the solvent composition is discussed in terms of the free energy transfer from water to ethanol-water mixtures. It is concluded that the specific solute-solvent interactions play a vital role in changing the pK values in ethanol-water mixtures.