This investigation This investigation was started by the synthesis of four pyridine Schiff bases from the mother compound (Salicyladehyed), whose nomenclatures and structures are seen in the text. The structures of these imines were well confirmed from U.V. and I.R. spectra at melting points. The main objective of this study is the determination of Ka values for these mentioned imines at temperature range (20-60) Co by the conductivity measurement method.This method as found, Simple, precise and accurate. The thermodynamic parameters of ionization for acids were also estimated. This shows that the process of ionization of acidic compounds under study in water Solvent is non-spontaneous ( +∆H) and is accompanied by an increase of order ( -∆S). Direct linear plots were obtained between pka for any acid versus the dielectric constant of acid and versus the dietetic constant of ethanol at the five different temperatures. Finally, a suitable interpretation for any one of these thermodynamic parameters are given and discussed.