The effects of the gel-forming polymer AgroAquaGel 500, added at doses of 1 and 2 g·kg^-1, on aggregation, aggregate water stability, and water and air properties of eroded Haplic Luvisol developed from loess, were investigated in a field trial. In the first year after the application of AgroAquaGel 500, a significant reduction of the unfavourable content of clods >10 mm was noted compared to the control, while air-dry aggregates of 0.25-5 mm and water-stable aggregates of 0.25-10 mm increased within the 0-5 cm layer of the eroded soil. The addition of the hydrogel to the soil significantly decreased its bulk density and increased its maximum water capacity, saturated hydraulic conductivity, total porosity, the content of macropores with diameters >20 μm, and air permeability. Whereas the beneficial after-effect of the hydrogel applied at the rate of 2 g·kg^-1 on aggregate size distribution and aggregate water stability was also seen in the second year, no significant influence was observed in the third year after its application. Values of Dexter’s index S for soil treated with AgroAquaGel 500 indicate the high quality of its water and air properties.