Abstract: Seasonal variations of soil inorganic nitrogen (N) pool and net N transformation rate in mosscovered soil and in the bare soil were comparatively observed by incubating intact soil columns with parafilm capping in the field in a natural vegetation area of Shapotou, southeastern fringe of the Tengger Desert. We found pronounced seasonal variations in soil available N content and net N transformation rate in both mosscovered soil and bare soil, with significant differences among different months. In nongrowing season, soil available N content and net N transformation rate were significantly higher in March and October than in other months. Furthermore, immobilization was the dominant form of N mineralization, and no significant difference in net soil N mineralization rate was found between the two sampling soils. In growing season, soil available N content and net N transformation rate markedly increased and reached their peak values during June to August (17.18 mg·kg^-1 and 0.11 mg·kg^-1·d^-1, respectively). Both soil net nitrification and N mineralization rates in mosscovered soil were significantly higher than in bare soil. Soil ammonium and nitrate N content in April and May were higher in mosscovered soil (2.66 and 3.16 mg·kg^-1, respectively) than in bare soil (1.02 and 2.37 mg·kg^-1, respectively); while the tendency was the converse in June and September, with 7.01 mg·kg^-1 for soil ammonium content and 7.40 mg·kg^-1 for nitrate N content in bare soil, and they were 6.39 and 6.36 mg·kg^-1 in mosscovered soil, respectively. Therefore, the existence and succession of moss crusts could be considered as one of the important biological factors affecting soil N cycling through regulating soil available N content and promoting soil N mineralization process.