The esterification of acetic acid and ethanol in compressed CO2 was studied at 333.2 K and at pressures up to 16 MPa, and the original. molar ratio of the components was CO2: CH3COOH:CH3CH2OH:p-toluenesulfonic acid (catalyst) = 90.5:5:0.05. The phase behavior and the isothermal compressibility (k(T)) of reaction system was also determined under the reaction conditions. The conversion increases with increasing pressure in the two-phase region and reaches a maximum in the critical region of the reaction system where the system just becomes one phase. Then the conversion or apparent equilibrium constant K-x decreases with pressure after the pressure is higher than the critical value. In the supercritical region where the system is one phase, K-x is closely related to the isothermal compressibility and degree of inhomogeneity of the fluid, which is often referred to as the local density and/or local composition enhancement. At the higher pressures the "clustering" in the reaction system is not significant and the K-x is close to that of the reaction in the absence of CO2.