Aerated concrete samples of two sizes(4cm×4cm×2cmand 3cm×3cm×1cm) were dried with desiccant at room temperature and with oven at 70℃ and 105℃ respectively. The dry masses obtained from different drying methods were compared. Static gravimetric method was used to obtain the equilibrium moisture contents in samples dried in oven at 70℃ in different relative humidities, and a statistical comparison was made. Peleg model was used to fit the moisture absorption isotherms of aerated concrete. Results reveal that the dry mass obtained from oven drying method at 70℃ is 0.13%0.16% greater than that obtained from desiccant drying method at room temperature, while oven drying method at 105℃ gives 102%106% smaller dry mass. Moreover, the equilibrium moisture contents in samples of different sizes under the same relative humidity are not the same. In middle high relative humidity range, the equilibrium moisture contents in smaller samples are noticeably less. The fitted moisture absorption isotherms of samples with different sizes and drying methods are noticeably different. The one for bigger sample dried in oven at 70℃ is recommended as the moisture absorption isotherm of aerated concrete.