Tetrabutylammonium bromide, a weak organic salt, is used as a phase-transfer catalyst in a phase-transfer catalytic reaction producing the desired product, benzyl bromide in the organic phase. The solubility of tetrabutylammonium bromide in benzene (used as the organic phase solvent) is the possible dominant factor influencing benzyl bromide yield. In this study, the solubility of tetrabutylammonium bromide in benzene was measured in the temperature range between 298.15 K and 323.15 K, and a theoretical approach for the solid-liquid equilibrium of this binary mixture was proposed. The experimental data were then correlated with the Pitzer-Debye-Huckel equation, accounting for the ionic interaction, and with the UNIQUAC model, taking into account the ion-molecule and molecule-molecule interactions. An empirical parameter was introduced to represent the degree of partial dissociation of tetrabutylammonium bromide into ions in the solvent.