The purpose of this investigation is to clear the effect of farmyard manure (FYM) on the nitrogen uptake, the nitrogen fixing capacity and the seed yield of nodulating soybean. In order to estimate the amount of fixed nitrogen, nodulating and non-nodulating isogenic lines were grown at same condition in 1/5000 are Wagner pot containing 3 kg of mineral soil with some levels of FYM or urea. The results obtained were as follows. 1. It was observed at the flowering stage of growth that the inhibitory effect of FYM on the nodule formation was clearly weaker than that of urea, and the number of nodules, the fresh weight of nodules and the amount of fixed nitrogen per plant were the largest at the application of lower level of FYM (80g fresh weight per pot). The nitrogen fixing capacity per unit fresh weight of nodules at flowering stage also increased with the level of FYM, although the higher levels of FYM (200, 400 and 1200g per pot) were unfavorable for the nodule formation. 2. Such an inhibitory effect of FYM on the nodule formation gradually diminished with aging. It was also observed at the harvesting time that the application of FYM in the ranges of 80g to 400g per pot led to the increase in seed yields accompanied with the larger amount of fixed nitrogen and the higher ratio of secd nitrogen to total nitrogen uptake, without diminishing the ratio of fixed nitrogen to total nitrogen in plant. 3. It was therefore presumed from this experiment that the application of FlM resulted in the increase of seed yields through thc improvement of symbiotic nitrogen fixation rather than the supplemental supply of available nitrogen released from FYM.