In this study, concentration of quaternary salt in a dichloromethane (or chlorobenzene)/water system were measured by extractive-titration method. Relevant thermodynamic data of these systems were also calculated. The true extraction constant, distribution constant, dissociation constant in the aqueous phase, mean activity coefficient, and free energies of the true extraction constant, distribution constant, and dissociation constant were obtained as well. A numerical model based on the concept of varied activity coefficient was designed to calculate the distribution constants and dissociation constants of these quaternary salts.