Abstract: With temperature and suction control, the evaluation of microstructure of densely compacted GMZ01 bentonite under different constraint conditions is conducted under wetting/drying cycles. The results indicate that for high suction (> 5 MPa), there is a significant difference between the effects of the drying/wetting cycles on the inter-aggregate pores and the intra-aggregate pores. Following the wetting path, all the pores with different sizes expand at different levels. While following the drying process, some inter-aggregate pores with larger size (>3000 nm) shrink, but the intra-aggregate pores almost do not change with the increase of suction. For confined GMZ01 bentonite specimen, when it hydrates to 5.1 MPa, the swelling of aggregates squeezes into the large pores, which causes the volume of inter-aggregate pores to reduce rapidly. However, the volume of the intra-aggregate pores almost unchanges. After that, when the specimen dehydrates to 103 MPa, the volume of intra-aggregate pores still unchanges. While the inter-aggregates pores differentiate, some of the lager pores (＞2000 nm) shrink into smaller pores (300 nm