The impact of different sizes of soil aggregates on the hysteresis of their water retention characteristics was determined. Soil aggregates were separated from the arable layer of Orthic Podzol, Eutric Cambisol and Haplic Phaeozem. The results of the study showed that the impact of aggregate size was significant. It was found that differences in water content during the drying and wetting processes varied not only for the chosen soil water potential and aggregate size, but also for the type of soil. The maximum differences in water content between the drying and wetting processes at the same soil water potential reached nearly 15% vol. in absolute values. Thus it can be stated that negligence of the hysteresis effect can cause inaccuracy of estimation of soil moisture.