The excess enthalpy H^E_m is important in order to understand the mixed state of fluids and intermolecular interaction. The behaviors of H^E_m of a binary mixture in the liquid state, near the critical points and gas state are quite different each other. In this article, the characteristics of the behaviors of H^E_m in each state are summarized briefly, and the cause of the difference in each characteristic is discussed in terms of the difference of the main factor of intermolecular interactions affecting the behavior of H^E_m. At first, the behaviors of H^E_m of binary mixtures containing aromatic or alcoholic molecular are described. The influences of the π-π interaction and the hydrogen bond on H^E_m are discussed over a wide range of temperature and pressure in the liquid state. Next, the specific behavior of H^E_m at near the critical points are discussed with respect to the relation of the experimental states of H^E_m to the location of the critical points, the vapor pressure curves and their extended curves of component fluids on the p-T plane. Finally, The contribution of the dipole moment and the polarizability of component molecules to the behaviors of H^E_m at gas state is discussed by comparing H^E_m of polar molecules + benzene or cyclohexane mixtures.