With the development of the chromatographic determinations in parallel with their analytical applications, non-analytical applications also came into use. The HPLC methods are widely used for the quantitative determination of drug preservatives, but they can also be used for the determination of the preservatives` physicochemical properties. The HPLC method is applied for determination of the pKa values and the lipophilicity parameter of the most useful preservatives in drugs oral solution formulations at different pH ranges. The same method is used for investigation on the lipophilicity of these compounds. The pKa and lipophilicity parameter values are the most important parameters characterizing the processes of penetration of preservatives through the cellular membrane at different conditions. The higher lipophilicity contributes to the better interaction of the preservatives with the membrane of the undesirable microorganisms and assures their biological action.