The dissociation constant (pKa) and thermodynamic parameters (60) of 8-methylquinoline are determined in aqueous and in mixed organic-water (Dioxane, EtOH and MeOH) solvent systems. It is observed that dissociation constant of 8-methylquinoline in aqueous system decreases with the increase of temperature. The curve shows some what linear decrease from 10% to 50% composition of solvent. It is to be. noted that pKa values of this compound are lower than quinoline and some of its methyl derivatives. For mixed organic-water solvent systems concentration ionization constant pI<. M and thermodynamic ionization constant pKa values versus percent composition decrease slowly with increase in percent of EtOH, MeOH and Dioxine. The curve of the pKa. verses percent composition shows some what linear decrease in this range.The data have been obtained potentiometrically by titrating aqueous 8-methylquinoline solutions with hydrochloric acid. The values of dissociation constant were obtained from these data by a computer program written in GW-BASIC. From pKa. values Gibb's free energies 60 for the respective pKa values have also been calculated.