A two-year greenhouse pot experiment was carried out by planting rice with 15N labeled fertilizers, urea, KNO3 and leguminous green manure (vetch) . The results are as follows1. Application of inorganic fertilizers in flooded soil (1986), whether urea or KNO3, led to increase of soil-N uptake by rice, the percentage increase over the control were 3.4-12.7 or 13.0-28.9 respectively when applying KNO3 or urea. For such effect, (1) Urea was superior to KNO3; (2) Deeper mixed application of each fertilizer was also correspondingly superior to the two surface placements done with each fertilizer.2. Rice plant-N derived from soil, which continuously increased throuthout the whole growth period, was 21. 9% to 31.0% (urea) and 26. 4 % to 40. 8% (vetch) from the six-leaf tu the fully mature period.3. As to increasing soil-N uptake by rice,vetch material performed better than urea,while the total soil-N uptake by rice with application of urea or ground vetch material was higher than that of the unfertilized control during the whole growing season of 1987.4. Whether chemical N fertilizers were applied or not, or no matter what forms of chemical N were applied, loss of original soil-N inevitably occurred when planting rice in flooded soil. The proper application of organic fertilizers was favourable to the maintenance of original soil-N, as well as the increase of soil fertility.