Abstract: After a series of laboratory experiments in an open system, the impacts of freeze-thaw cycles on the structure of compacted loess are studied by means of the quantitative analysis of scanning electron microscope images. The physical properties of the soils are tested simultaneously to discuss the relationship between microstructure and macro-properties of the loess. The results of microstructure analysis show that, with the increase of freeze-thaw cycles, the formation of cryogenesis results in obvious enlargement of pore volumes and therefore extrusion and redistribution of soil particles. The ratio of big- and mid- pore area to the total pore area increases from 78% after 2 cycles to 90% after 31 cycles. Meanwhile, some pores with open structure, which controls the loess collapsibility, are formed during the cycles. The results of macro-properties test show that, during the cycles, the water content of the samples increases significantly and is redistributed, and the dry density of the samples decreases initially and then keeps almost constant. After 31 cycles, the water contents at the upper and lower parts of the sample increase by more than 140% and 55%, respectively, whereas the dry density of the sample decreases from the initial value of 1.86 g/cm³ to 1.55 g/cm³, about a depression of 17%. Collectively, the results from both the micro- and macro-analyses indicate that the freeze-thaw action significantly weakens the structure of compacted loess.