Abstract Conductometric titrations with triethylamine (Et3N) of mono-, di-, and trisulfonic acids have been performed in acetonitrile, and strong homoconjugation (homoassociation) for di- and trisulfonic acids have been revealed. The appearance of a maximum in the conductometric titration curve enables us to predict the stable homoconjugation species in the solution. The homoconjugation reaction of monosulfonic acids, such as methanesulfonic and p-toluenesulfonic acids, are not large enough to give a maximum. However, disulfonic acids, 1,5, 2,6-, and 2,7-naphthalenedisulfonic acids, give maxima at the first equivalence point, which indicates that the conjugate ions (HA−) cause homoconjugation reactions. By means of UV–visible spectroscopy, the stability constant (KD) of dimerization or homoconjugation reaction between two anions [2 HA− <img align="middle" src="./Graphics/abst-87_20130176_1.png"/> (HA−)2] of the hydrogen 1,5-naphthalenedisulfonate (HA−) has been given to be log KD = 4.11 in acetonitrile. In the same solvent, 1,3,6-naphthalenetrisulfonic acid forms more stable species of not only (H2A−)2 but also (H2A−)(HA2−). Double hydrogen-bonds can operate between two H2A− anions in the (H2A−)2 species, while even triple hydrogen-bonds in the (H2A−)(HA2−) species. Effects of second solvents, including H2O, have been examined in detail on the homoconjugation reactions. In order to differentiate the role of acidities of acids on homoconjugation, the conductometric titrations of nitrobenzenedicarboxylic acids have been also performed. The geometries of homoconjugated sulfonic acids have been justified by DFT calculations.