Solid-liquid equilibria of three binary mixtures consisting of benzoic acid, 2-aminobenzoic acid and 1-naphthol were measured in this study using differential scanning calorimetry (DSC). Simple eutectic phase diagrams were observed, and the experimental data were well correlated by either the Wilson equation or the UNIFAC activity coefficient model. A new method by employing the DSC experiment and the theoretical calculations to detect the fractional transformation of solid-liquid equilibrium of organic mixture is proposed. Deconvolution method was employed to obtain the ideal equilibrium solid-liquid DSC curve. The heat generation rate and fraction of transformation were calculated using the Gray's model. Applying this theoretical approach, the eutectic points and the equilibrium liquidus temperatures were easily determined from the fractional transformation curve. An easier procedure to confirm the composition of eutectic point is presented. It is also demonstrated that the solid-liquid equilibrium phase boundaries are predicted with good agreement to the experimental results.