The research was conducted on standard soil aggregates of 1 cm3 density and moulded structure in air-dry state, in rigorously controlled moisture and compaction conditions. On these aggregates such properties as dynamic and static -water resistance, the state of aggregation after dynamic and static water action, the speed of capillary rise and capillary water capacity, so soil structure-forming best characterizing parameters, were marked. These properties were researched on aggregates moulded from the soil material taken from arable horizons of gray-brown podzolic soil (loamy sand) and black earth (sandy loam). As an addition to soil, 4 doses of hydrogel were used in the amount of 0.033; 0.066; 0.132 and 0.264% in dry soil mass. The conducted research proved positive influence of hydrogel on the analyzed physical-mechanical parameters of soil aggregates, regardless of the material they were moulded from. In general, the doses of hydrogel used caused the decrease of soil bulk density and therefore, porosity of aggregates was increasing. In spite of the decrease of dynamic water resistance, secondary aggregation, i.e. the number of aggregates bigger than 0.25mm, was growing within the range of 5-7% along with the increase of the dose of means. Moreover, resistance to static water action improved, and the number of secondary aggregates grew up by 6-12%. The time of water translocation in aggregates decreased significantly, i.e. even twice or thrice. When the time of capillary rise is concerned, maximal capillary capacity increased by I9%v/v in loamy sand (gray-brown podzolic soil) and by over 13%v/v in sandy loam (black earth). This beneficial influence of hydrogel on structure-forming parameters, especially water properties, was confirmed in field researches. On experimental plots with the growing of pea, with the employment of spray irrigation, hydrogel added to soil caused the growth of the crop from 37.8 dt/ha (control) to 46.6 dt/ha (100 g/m2 dose), so by more than 23%.