The main objective of the studies was to determine the changes of microbiological activity and content of the labile fraction of organic matter (POM) in soils under reduced tillage and no-tillage systems, as compared to the conventional tillage. At a private farm in Rogów the content of microbial biomass C was about 13 and 8% higher in soil under no-tillage and reduced tillage, respectively, than in soil managed in the conventional manner. Similar trends in microbial biomass C content were noticed in the soil sampled from the fields in Żelisławki. Microbial respiration, measured under laboratory conditions as the intensity of CO2 evolution, was higher in soils under no-tillage than under conventional tillage in Rogów and Żelisławki, at up to 30 and 22% (on average), respectively. The highest values of the activity of dehydrogenases were obtained also in soils under no-tillage system at both experimental sites. The microbial quotient (microbial biomass C/Corg ratio) showed the highest values in no-tillage soils, but the metabolic quotient qCO2 in conventionally managed soils at both experimental sites. The increase of POM fraction expressed as a percentage of total OM was higher by about 34% in Rogów soil under no-tillage, as compared to the soil under conventional tillage. Also, in Żelisławki, a higher increase of POM in total organic matter content was observed in soil under conservation tillage systems (reduced and no-tillage) than under conventional tillage, by about 10-15%.