As it is well known, the share of microorganisms in the fertility and soil health is very important. Soil microorganisms play a major role in organic matter mineralization, provide nutrients to plants, and improve the soil structure. The size of the soil organisms is very variable. It depends primarily on the water and air relations in the soil as well as the temperature. The aim of the research was to determine the content of live microorganisms biomass in the soil under rape, maize, bean and wheat crops including the rhizosphere. The analyzes were carried out in different vegetation periods and phases of plant development on the example of the farm in Starza. Determination of living microorganisms biomass was carried out applying the method developed by Anderson and Domsch. The biomass content of live microorganisms in the soil was dependent on the cultivated plant, growing date and phase, as well as the proximity of the rhizosphere.