Quantity of some groups of microorganisms and dehydrogenase activity were determined in the top soil layer (0-10 cm) of natural and drained peatland. High soil moisture (85 to 90%) in the natural peatland accounted for the reduction of fungi and cellulolytic microorganisms which can reflect a restricted process of peat mineralization. In late summer (September), peat-muck soils of drained meadows supported rather high numbers of cellulolytic microflora, except for the Modzelówka peatland that was highly decomposed. In the alder peat with high degree of mucking and low moisture content (55-63%), fungi were abundant. Dehydrogenase activity was the highest (153 to 181 µl H₂ g^–1) in natural peats with high moisture content (80-89%) and the lowest (5-13 µl H₂ g^–1) in alder peats with high degree of mucking. Thus, moisture and degree of peat mucking affect development of microorganisms and dehydrogenase activity causing more or less intense mineralization of organic matter.