Laboratory analysis was conducted to investigate nitrogen mineralization of soils in the Loess Plateau of China.The aims of our study were to determine the content of SON(soluble organic nitrogen),and the percent of TSN(total soluble nitrogen) to SON,and the relate SON to mineralized nitrogen.Results showed that the content of SON of all soils increased significantly during incubation.The percent of TSN to SON was the highest at start stage.From day-0 to day-3,the percent declined to the lowest level.After that the percent increased gradually.In the end of incubation,SON accounted for 24% of TSN.Soil mean mineralization potential(N0) based on total soluble nitrogen(45.8 mg/kg) was a quarter higher than mean mineralization potential(36.5 mg/kg),which was based on mineralized inorganic nitrogen.The positive relationship was found between the content of SON and mineralization potential that based on mineralized inorganic nitrogen,but not reach significant level.Our results suggested that in order to evaluate nitrogen mineralization,the content of SON was only measured during incubation may underestimate mineralization potential and the amount of nitrogen losses.