Abstract: This work was carried out by field experiment in 1961 and 1962 to study the effect of nitrogen-level upon the metabolism, growth, and yield of rice. The main results obtained were as follows: 1. The yield of rice increases proportionally to the nitrogen level below 10–15 kg/mou. The high nitrogen level increases the number of spikes, but decreases the number of grains per spike and the weight per 1000 grains. 2. The effect of the amount of nitrogen applied on the growth was different with various organs. After the differentiation of panicle, the high level of nitrogen retards the growth of sheath and stem, but promotes the growth of leaf blade. Hence the sheath/leaf ratio decreases with the increase of nitrogen level. When the sheath/leaf ratio is higher, the weight per 1000 grains and the grains per spike increase also. 3. The carbohydrate and nitrogen metabolism is varied with the amount of nitrogen applied. Starch accumulates more in the sheath and stem at the lower nitrogen level. At the time of heading, the starch translocates from the sheath and stem to the spike. On the basis of this investigation, it may be suggested that the sheath/leaf ratio and the dynamic accumulation of starch in the sheath and stem could be used as the physiological indication for the application of nitrogen fertilizer.