Thermodynamic properties of adamantane (I) were investigated in this paper. Heat capacities of I in the condensed state between 340 and 600 K were measured by a scanning calorimeter of triple heat bridge type, and characteristics of the fusion of I were determined. The measurements of the enthalpy of sublimation and the saturated vapor pressure for I were made. Thermodynamic functions of I in the ideal gas state were calculated by the statistical thermodynamics methods. The energy stares of molecules in the plastic crystals for some cage hydrocarbons (adamantane, bicyclo[2.2.2]octane, pentacycloundecane, heptacyclotetradecane and diamantane) are discussed.