Heat capacities of (-)-DIOP have been measured with a precision automatic adiabatic calorimeter in the temperature range from 78 to 380 K. A solid-solid phase transition for the compound was observed at 338.65 K and the molar enthalpy and entropy of the transition were determined to be 3.415 kJ mol(-1) and 9.795 J mol(-1), respectively. A solid-liquid phase transition was found at 364.23 K and the molar enthalpy and entropy of fusion were determined to be 38.606 kJ mol(-1) and 106.0 J K-1 mol(-1) respectively. The purity of the sample under investigation was determined to be 0.9837 molar fraction by the fractional melting method.