Heat capacities of (1R,2S,5R)-2-i-propyl-5-methylcyclohexyl diazoacetate have been measured with a small sample adiabatic calorimeter over the temperature range from 78 to 344 K. The melting point, molar enthalpy and entropy of fusion as well as the chemical purity of this compound were determined to be 320.419 +/- 0.017 K, 17.203 +/- 0.005 kJ mol(-1),53.689 +/-0.013JK(-1) mol(-1) and 99.61 mol%, respectively, on the basis of the heat-capacity measurements. The extrapolated melting temperature for the absolutely pure compound obtained from fractional melting experiments was 320.602 K.