In this paper, the relations of nitrogen application at four stages with different amounts to accumulation of protein in brown rice were studied by soil cultivation and ¹⁵N tracing technique. The results showed that applying N at booting stage was most favourable to the accumulation of protein in brown rice and the ratio of ¹⁵N protein-N in brown rice to applied ¹⁵N reached 36.15%. This effect of applying N before transplanting took second place, and those at tillering stage and milk stage were relatively disappointed. The results also demonstrated that, under the condition of fixation of N application at the rest 3 stages,¹⁵N applied at one stage was significantly linearly correlative with ¹⁵N protein-N in brown rice, but the relation between N application amount at all 4 stages and total protein-N in brown rice presented a parabolic curve, because of the decrease of brown rice yield and the descent of protein-N content under the condition of excessively applying N.