In Cixi of Zhejiang Province, as a result of poldering in different time periods a long time scale succession of paddy soils and upland soils formed, which could be cited as good objects for the study of long term biogeochemical cycle of soil nitrogen. In order to explore effects of cropping history and pattern on soil organic nitrogen fractions, amino acid N, amino sugar N, NH₃ – N and hydrolyzable unknown N in the soils were analyzed with the Bremner method through hydrolysis in sealed tubes. Results show that the content of any fraction of organic nitrogen in the upland soil was only 50% ~ 60% of that of its counterpart in the paddy soil, suggesting that rice planting is more conducive to conservation and utilization of the soil organic nitrogen. On a long-time scale, all the organic nitrogen fractions, except amino acid N and amino sugar N, varied with the time exponentially, showing that organic nitrogen in the paddy soils was mainly on a rising trend, while that in the upland soils on a reverse one. In the soils of this area, amino acid N accounted for 23.5% ~ 29.3%, amino sugar N for 6.0% ~ 7.6%, NH₃ – N for 21.0% ~ 28.8%, and hydrolysable unknown N for 13.0% ~ 21.1% of the total nitrogen, indicating that cropping pattern and cropping duration neither has much effect on proportions of the major soil organic nitrogen fractions to the total nitrogen in the soils.