The aim of the research was to complement the knowledge on profile distribution and accumulation of phosphorus forms in the soils changed under the influence of secondary organic matter transformation process in dehydrated peatlands. The soil research was carried out in the upper Liwiec river valley in the middle-east of Poland. In the soil material taken from the moorsh (M1, M2, M3) and peat (O) horizons of the Murshic Histosols, the physical and chemical properties were determined and the soil phosphorus fractions with different activity in the environment by sequential extraction method were separated. The profile distribution of the total phosphorus content (TP) and values of carbon/phosphorus (TC/TP) ratio were characteristic for dehydrated peat soils included in the secondary transformation process (M1>M2>M3>O). This process also increased the contribution of the available phosphorus forms (NH4Cl-P), forms bound on the surface of iron (III) and manganese (IV) oxides and hydroxides (redox-P), as well as mineral (mHCl-P) and organic (oHCl-P) forms separated by 0.5 M HCl. Significant accumulation of the phosphorus compounds in the moorsh horizons of the investigated soils can be considered as a potential threat to the natural environment of the studied area due to the risk of decomposition of the phosphorus compounds when the area will be rehydrated.