The effect of aggregate size on hydraulic conductivity coefficient of two tilled soils with different genesis and the same texture is presented. The distribution of values of the hydraulic conductivity coefficient of Haplic Phaeozem relative to the particular aggregate fractions displays a bimodal character similar to that of the pore size distribution. The values of hydraulic conductivity coefficient for fraction of <0.25 mm of Eutric Fluvisol are significantly higher than those for the remaining fractions. For the aggregate fraction of <0.25 mm of Eutric Fluvisol and for the aggregate fractions of <0.25 and 0.25-0.5 mm of Haplic Phaeozem the dominant mechanism of water flow is the inter-aggregate transport, while for the remaining (larger) aggregate fractions of both the soils the dominating flow mechanism is the intra-aggregate transport of water.