In this study, the thermodynamic dissociation constants of two new quinoline derivatives including (6-hydroxyl-3-sulfoquinoline-7-yloxy) acetic acid and (5-bromo-6-hydroxyl-N-methyl-3-sulfoquinoline-7-yloxy) acetic acid were initially determined in an aqueous solution using potentiometric titration at (25.0 ± 0.1) oC in the ionic medium of 0.10 M KCl solution. From the results of this research, the dissociation constants of (6-Hydroxyl-3-Sulfoquinoline-7-yloxy) acetic acid are pKa1 = 4.15 ± 0.01 (for COOH group), pKa2 = 8.72 ± 0.02 (for NH+ group) and pKa3 = 10.76 ± 0.03 (for OH group) while the pKa values of 5-bromo-6-hydroxyl-Nmethyl-3-sulfoquinoline-7-yloxy) acetic acid is pKa1 = 2.59 ± 0.02 (for the COOH group) and pKa2 = 5.41 ± 0.03 (for the OH group). To increase the reliability and accuracy of the results, the pKa values could be calculated at different concentration levels. The structure of quinoline derivatives and data of potentiometric titration were analyzed in detail before calculating and assigning the pKa values to suitable functional groups. These results will be applied to our further studies of these compounds.