Solid-liquid equilibrium (SLE) behavior was observed for close-boiling mixtures of 4-methoxyphenol and catechol with tert-butanol. The experimental liquidus lines of binary systems showed that intermolecular complex compounds were formed in both tert-butanol/4-methoxyphenol and tert-butanol/catechol, implying that tert-butanol is a potential medium to serve as an adductive agent for separation of 4-methoxyphenol and catechol. A ternary SLE phase diagram for the tert-butanol/4-methoxyphenol/catechol system was thus prepared and, based on the diagram, the feasibility of such separation processes was discussed. Furthermore, the binary SLE data were correlated with the ideal-chemical model. The model with the determined parameters from binary mixtures was then applied to predict the equilibrium temperatures for the ternary system.