Excess molar enthalpies HE for two ternary systems, 3-methylphenol-phenol-n-heptane and 3-methylphenol-l-hexanol-n-heptane and a constituent binary 3-methylphenol-n-heptane have been measured with Calvet-type microcalorimeter at 318.15 K. For predicting ternary excess enthalpies, the modified Redlich-Kister equation was used. It has been shown that the second ternary system exhibits regions of both exothermic and endothermic mixing, and due to the intricated interaction between phenols and alcohols predicting of ternary excess enthalpies with the Redlich-Kister equation is unsuccessful.