The research was conducted on the material taken from the arable-humin horizons of three soils (two Luvisols and one Phaeozems). The incubatory experiment was carried out in laboratory conditions in the bowls of 7 dm3. The bowls contained 4-kilo soil samples which had been mixed with three dozes of effective microorganisms (EM-A preparation of 0,4 cm3, 0,8 cm3 and 1,6 cm3, respectively). After a six-week incubation held in strictly controlled conditions of soil temperature and air temperature and humidity, 50 aggregates of 1 cm3 capacity were cut out ofeach combination. Basic physical properties such as density andporosity as well as structure-forming parameters (water resistance, compressive strength, water capacity). It was proven that values of the listed parameters depend mainly on the applied dozes of effective microorganisms and to a smaller extent on soil graining and compaction. From both economical and practical points of view, the second dose of EM turned out to be the most effective for the majority of soil`s physicomechanical properties.