1. Negative correlation was found between the total N absorbed by rice and F/T (The ratio of fertilizer N absorbed by rice to total N absorbed by rice) in four paddy soils of Jiangsu Province. It means that the more the N uptake by rice, the less the proportion of fertilizer N in the total N uptake. 2. Regular distribution of three levels of rice yield was found in the figure on which the. total N uptake by rice was plott ed against F/T. It was shbwed that the high yield of rice was mainly dependent on soil nitrogen. 3. Isotopic study showed that contrary to the inorganic fertilizer N, the recovery of organic fertilizer N in grain was higher than that in straw. 4. It was found that the duration of nitrogen supply from inorganic fertilizer could be lasted when it was mixed with organic matter. In present experiment, the N supply status of inorganic fertilizer nitrogen seemed to be similar to that of organic fertilizer nitrogen. 5. The fate of inorganic and organic fertilizer nitrogen applied in rice-soil system has been determined respectively after harvest.