The phase behaviors, constant volume heat capacity (C-v), and isothermal compressibility (K-T) of ethane + ethanol and ethane + acetone binary mixtures have been measured in supercritical (SC) region and subcritical region near the critical point (CP) of the mixtures at 309.45 K. The experiments have also been carried at the conditions far from the critical point of the mixtures. It is demonstrated that in supercritical region there exists a maximum in C-v versus pressure curve (C-v(max)) at fixed composition, which occurs at the pressure where K-T is the largest. In subcritical region, C-v and K-T increase sharply as pressure approaches the critical point or bubble point (BP), and the C-v at CP or BP can be several times larger than that of the fluids far from the phase separation pressures. On the basis of the experimental results, the intermolecular interaction is discussed. (C) 2003 Elsevier B.V. All rights reserved.