Today, the traditional agriculture employs increasingly frequently unconventional preparations such as solutions of Effective Microorganisms (EM) to improve soil fertility. These types of preparations are believed to exert a number of positive effects including increased soil fertility. However, the application of Effective Microorganisms arouses numerous controversies. That is why initial experiments were undertaken with the aim to assess possible influence of an EM preparation on physical-and-chemical and chemical properties of arable soils. The aim of the study was realized on the basis of investigations employing two soils - Luvisols and Phaeozems - which were incubated with increasing doses of the experimental EMA preparation. The results of the performed experiments failed to confirm a positive impact of Effective Microorganisms on quantities of organic carbon, humus or increase of soil pH. Increasing doses of the EM-A preparation were found to increase quantities of available potassium, magnesium, sulphur and mineral nitrogen and to decrease S and PWK values in the examined grey-brown podzolic soil. On the other hand, in the case of the proper black earth, concentrations of available potassium, magnesium, sulphur and mineral nitrogen as well as hydrolytic acidity decreased, while S and PWK values increased together with the dose increase of the applied conditioner.