Activity of dehydrogenases (DHs) indicates the presence of viable and physiologically active (physiologically active or physiological activity) microorganisms. Their presence (activity) in soil is correlated with the content of organic carbon, microorganisms, nitrifying activity and microbial respiration. Determination of DHs activity allows to control changes in soil microbial population and is considered as an important parameter of soil quality. The aim of the study was to determine the effects of different farming systems on the enzymatic activity in soil under winter wheat. The research was conducted in the years 2014–2016 on long-term field experiment under two different farming systems (ecological and conventional) at the IUNG (PIB) Experimental Station located in Osiny (Lublin Voivodeship), Poland. Each farming system differs in crop rotation system and whole agrotechnics, which have been adapted to its specificity. Determination of DHs activity was performed using Casida et al.’s (1964) method with modifications. Measured DHs activity was expressed in milligrams of triphenyl formazan (TPF) per 100 g of soil within 24 hours. The results showed that ecological farming system beneficially influenced soil environment.