For the study a cultivated Haplic Luvisol (typical soil lessivé) derived form loess was chosen. Undisturbed samples were taken from the layer of 0-8 cm in the vertical plane into metal boxes measuring 8×9×4 cm. The samples were used to prepare opaque polished blocks. The opaque blocks were arranged in the sequence from the soil of coherent and porous structure to the soil of relatively homogenous aggregate-fragment structure, creating an array illustrating a hypothetic formation of an aggregate structure. On the basis of the processed photographs of opaque block faces the computer-aided image analysis was performed. There were estimated: areas Ai, number N and perimeters Li of pore cross-sections; macroporosity AA; relative length of perimeters of pore cross-sections LA; relative number of pore cross-sections NA; average area of pore cross-sections AN. Using the values of AA and LA, the mean intercept length across pores and solid – λP and λS – were calculated. The most distinctive changes of the values of measured parameters, accompanying the changes of soil structure, were detected for AA, LA and λS. The most visible differences were detected in particular between the values of AA and LA for the three types of soil structure: I. structure of discrete pores, continuous solid phase and without aggregates; II. structure with pores of different character/genesis that traverse the soil material building less or more regular pattern, without aggregates; III. structure with pores that build well developed network, so aggregates – fragments – are formed.