Solid-liquid phase diagrams of two ternary mixtures containing polynuclear aromatic compounds, viz., cis-decahydronaphthalene (cis-decalin)-naphthalene-biphenyl and 1,2,3,4-tetrahydronaphthalene (tetralin)-biphenyl-dibenzofuran, have been measured at 298 K and 1 atm. These phase diagrams are also predicted using binary interaction parameters obtained from the regression of binary data alone using the UNIQUAC model and regular solution theory. It is observed that, by using binary parameters and UNIQUAC equations for multicomponent mixtures, one can predict the saturation curve for naphthalene within 7% and the saturation curve for biphenyl within 4% for the cis-decalin-naphthalene-biphenyl system. For the tetralin-biphenyl-dibenzofuran system, the saturation curve could be predicted within 4% for biphenyl and within 6% for dibenzofuran. Regular solution theory did not predict the saturation curves satisfactorily.