Three ternary Dy(III) complexes were synthesized with aromatic acids (p-nitrobenzoic acid, m-nitrobenzoic acid, and o-chlorobenzoic acid) as the first ligand and 1,10-phenanthroline as the second ligand. In accordance with Hess's law, a reasonable thermochemical cycle was designed, and standard molar enthalpies of dissolution for the reactants and products of the coordination reactions in the selected solvent were measured by a solution-reaction isoperibol calorimeter, respectively. In addition, the enthalpy changes of the coordination reactions were determined. Finally, the standard molar enthalpies of formation of the three synthetic coordination complexes were estimated to be Delta fH(m)(0)[[Dy(p-NBA)(3)phen](2)center dot 3H(2)O(s), 298.15 K] = (5177 +/- 8) kJ . mol(-1), Delta(f)H(m)(0)[[Dy(m-NBA)(3)phen](2)center dot 4H(2)O(s), 298.15 K] = -(5452 +/- 6) kJ . mol(-1), and Delta(f)H(m)(0)[[Dy-(o-ClBA)(3)phen](2)(s), 298.15 K] = -(5317 +/- 7) kJ . mol(-1).