The aim of this research was to determine the effect of applied tillage systems on changes of chosen parameters of soil microbiological activity. Analyses of microbiological properties of soil were performed on soil samples collected from long-term field experiments at a private farm in Rogów (Lublin voivodeship) on silt-loam soil and at the IUNG-PIB Experimental Station in Grabów (Masovian voivodeship) on heavy loamy sand. Winter wheat was grown in conventional (CT) and reduced tillage (RT) systems. Analyses of soil taken from experimental fields included the rate of CO2 evolution using the titration method; microbial biomass C content using the F-I method; dehydrogenase system activity using TTC as a substrate; microbial biomass N content using the F-E method and the Most Probable Number (MPN) of ammonia- and nitrate-forming bacteria. Applied tillage systems affected significantly the analysed parameters of biological activity of tested soils in both experimental years. In general, at both experimental sites, the numbers of specific groups of soil microorganisms estimated on the quantity of biomass C and N were significantly higher in RT soil than in CT soil (by about 20%, on average) at both depths: 0-15 and 15-30 cm. In 2006 and 2007, the dehydrogenase activity, ammonification and nitrification strength of soil reached the highest values mostly in RT soil at both experimental sites. Calculated higher values of microbial quotient and lower values of metabolic quotient in RT soil indicate that the RT system created a more friendly environment for the growth and activity of soil microorganisms, in comparison with the CT system.