In this study, heat and moisture transfer data of an enthalpy exchanger were obtained varying the indoor and outdoor condition systematically. At the same time, equilibrium water content ratios of the membrane were measured. It is shown that equilibrium water content ratio of the membrane increases with the increase of relative humidity. The effect of temperature on equilibrium water content ratio, however, is rather complex. It decreases with the increase of temperature to a certain value, and then increases with further increase of temperature. Moisture transfer effectiveness of the enthalpy exchanger is also affected by relative humidity and temperature. Heat transfer effectiveness, however, is independent of relative humidity and temperature. Moisture transfer effectiveness of the enthalpy exchanger was successfully correlated by equilibrium water content ratio of the membrane.