The paper discussed the application of mercury porosimetry method to investigations of agricultural materials. Most of these investigations concerned the soil materials. Pores systems of soils were characterized taking into account the pore classifications. The effects of polyamide sorbent on sandy and clay soils microstructure were investigated. Also the influence of mechanical deformations on the dimension of soils particle aggregates and on the microstructure of soil were described. The microporosity of humic fractions (humic acids and ß-humus) and internal porosity of wheat grain and starch extrudates were described.