The results of studies on the hysteresis effect of water retention curves of mineral and organic soils showed that Gleyic Phaeozem aggregates are characterized with a greater ability to retain water than are Haplic Luvisol aggregates. The highest values of moisture differences were noticed for 0.5-1 mm Gleyic Phaeozem aggregates at low soil water potential. The effect of hysteresis was small for aggregates of 3-5 and 5-10 mm in the whole range of the soil water potential and for pF higher than 1 for aggregates bigger than 0.5 mm. The maximum surfaces of the hysteresis loop were noticed for 0.5-1 and 0.25-0.5 mm aggregates of Gleyic Phaeozem and these were about 2.5 times higher than those for the aggregates of Haplic Luvisol.