Taking modified sodium bentonite, from Gaomiaozi, Inner Mongolia, as research object, the thermal aging, γ-rays irradiation aging, and radiation-thermal sequential aging were investigated by X-rays diffractometer and STA, separately. The corresponding effects on the property and microstructure of modified sodium bentonite demon-strate that the impact of either thermal aging or γ-rays irradiation aging is limited. However, the effect induced by ra-diation-thermal sequential aging is significant. After 1000 kGy γ-rays irradiation and thermal-aging for 9000 h at 120℃, montmorillonites have turned into illites; furthermore, crystal cells also have decreased from 15.8 nm to 6.0 nm or so in length. Therefore the thermal and γ-rays irradiation impacts should be considered in future research work.Cited