Hydraulic conductivity of soil is strongly dependent on soil structure, which can be degraded during wetting and leaching. It was hypothesised that this structural degradation is dependent on initial aggregate size distribution and soil texture. The general aim of this study was to investigate the effects of aggregate sizes and soil textures, and their interactions, on the structural degradation and saturated hydraulic conductivity (K_s) of smectitic soils under different saline and sodic conditions. The studied soils were clay and loamy sand soils with low (~4.5) or high (~10) exchangeable sodium percentages (ESP), and with aggregate sizes in the ranges: (i) <1 mm (small aggregates); or (ii) 2–4 mm (large aggregates). The K_s values of the samples in a column after slow or fast pre-wetting were determined by means of a constant head device. Different wetting rates and leaching under various saline and sodic conditions had no effect on the K_s of the loamy sand; however, the K_s values of this soil with large aggregates were an order of magnitude greater than those of the soil with small aggregates. In contrast, in the clay soil with large aggregates, the K_s values after fast pre-wetting were significantly smaller than those after slow pre-wetting, probably because of aggregate slaking. No significant effects of the wetting rates on K_s were found in clay soil with small aggregates. An increase in the ESP in the clay soil decreased the K_s by a factor of 1.5 for the large aggregates and by an order of magnitude for the small aggregates, mainly as a result of increased clay swelling. Leaching the clay soil with deionised water significantly decreased the K_s values, partly because of clay dispersion. Although significant structural degradation of the clay soil occurred during leaching, the K_s values were smaller in the soils with small aggregates than in those with large aggregates, indicating the importance of the initial aggregate size on K_s even in soils that are prone to structural damage.