The paper analyses characteristic structure-forming properties such as: the dynamic and static water resistance of soil aggregates, the secondary aggregation following the dynamic and static water action, capillary water capacity, volume changes caused by swelling and shrinkage of soil aggregates and their mechanical strength for six topsoil horizons of phaeozems. Experiments were carried out in carefully controlled moisture and compaction conditions of modelled soil aggregates of V=1 cm3. The aggregates were characterised by a considerable variability of texture, especially of the colloid fraction content (from 10 to 54%) as well as a significant variation in the content of organic matter (from 27.6 to 41.0 gźkg-1). Basically, the above two factors determined the structure-forming potentials of the examined soils. The secondary aggregation, following the dynamic and static water action, measured by the amount of secondary aggregates > 0, 25 mm, ranged from 26 to 89%. High retention potentials of the examined aggregates led to considerable volume alterations in the course of drying and moistening processes: shrinkage reached the value of 54%, while swelling attained the value of even 80% of the initial aggregate volume. Consequently, loosening or compaction of the aggregate solid state occurred, leading to their varying suscaptability to the action of external factors, including their resistance to the action of water and mechanical strains.