The mineralization of nitrogen in post-boggy soils with a wide range of soil organic matter- SOM (from 3% to over 80%) was studied. Laboratory aerobic incubation of soil samples taken volumetrically in the autumn period was carried out. According to N-NO₃ content after incubation one can state that moorshous formations have medium levels of available nitrogen, moorshes – medium to high, and peats – low. The relationship between N-NO₃ content and soil moisture (%, v/v) is parabolic. The highest nitrate content was found in samples with water content of 40-70%, v/v. The relationship between the quotient N-NO₃ : N-NH₄ and the water content displays a similar pattern. The rate of nitrogen transformation is higher in post-boggy soils with lower content of SOM than in soils having more organic matter. In moorshous soils mineral nitrogen after incubation constitutes 0.71% of total nitrogen, whereas in moorsh soils only 0.31%.