At the turn of the 19th and 20th centuries large peatland areas of the Stołowe Mountains were drained for the forestry use. The aim of the study was to assess the real impact of the natural (climate) and anthropogenic (forestry drainage) factors on the actual nitrogen mineralization in the shallow organic soils in the Stołowe Mountains National Park (SMNP). For the needs of the study, two research transects were established on the fen peatlands located in the central part of the SMNP. Each transect consisted of three sampling plots. The soil samples for the basic soil properties analysis were sampled in April, while undisturbed soil samples for mineral nitrogen were collected in April (spring), July (summer) and October (autumn) to show the seasonal dynamics of nitrogen mineralization. The obtained results revealed that the currently investigated fen peatland soils were rather slightly affected by the drainage network remains. A vast domination of ammonium over the nitrate form observed in the study soils during the growing season might indicate a periodical soil moisture increase limiting the mineralization process. The amount of precipitation and soil moisture had dominant impact on the N mineralization process, especially on the N-NO3 concentrations.