The heat capacity of 4,4′-dinitrodiphenyl ether and 4-nitro-4′-biphenylcarboxylic acid were measured by adiabatic calorimetry (AC) in temperature ranges of 8–372 K and 10–372 K, respectively. The heat capacity of 4,4′-dinitrodiphenyl ether in the temperature range 323–500 K, the thermodynamic properties of fusion, and the purity of the ether were measured by differential scanning calorimetry (DSC). The main thermodynamic functions in the temperature range 5–370 K were calculated for both compounds using the heat capacities of adiabatic calorimetry. Related thermodynamic functions of 4,4′-dinitrodiphenyl ether in the temperature range 370–500 K were calculated on the basis of DSC data.