Soybean, inoculated with effective Rhizobium japonicum 110, were grown by sand culture with nutrient solution containing either of 0,1,3,10 or 30 mM NO_3^-/l, and analyzed growth characteristics, NR activity, N_2-fixation activity, and changes of ureide contents during the growing period. The amount of nodule formation decreased abruptly by nitrate treatment, the maximum nodule dry weight was 1.59, 1.05, 0.78, 0.09 and 0.008 g plant^-1, respectively for each treatment on the 98th day. Specific activity of N_2-fixation showed the maximum rates of 140, 101, 37, 5 and 2.2 nM dw·㎎^-1·hr^-1, respectively for each treatment in the earlier growth period. The maximum acetylene reduction activity on the 98th day after sowing was 81.5, 35.3, 14.3, 0.1 and 0.0045 μM C_2H_4 plant^-1·hr^-1, respectively for 0,1,3,10 and 30 nM of NO_3^- gradients. Nitrate reduction activity increased along with nitrate gradients, and decreased abruptly with age. Relative abundance of ureides in plant organs was high in reproductive growth, and showed the maximum value in fully symbiotic dependent plant. Relative abundance of ureides in stem is a useful indication for the evaluation of nitrogen fixation in nodules of symbiotic plant.