A review on the effect of the plantation of aquatic plants on rice yield conducted by the authors in recent years is given.It is considered that the nitrogen cycle in the water layer is closely related to the nitrogen cycle in the underlying soil layer,and the plantation of aquatic plants in rice field showed beneficial effects on the nitrogen economy for rice growth.Another aquatic plant,pistia stratiotes,although does not possess the ability of fixing nitrogen from the atmosphere,reduced the loss of nitrogen brought in through irrigation water and fertilizers,and diffused from the underlying soil.The latter effect is quite important in decreasing the loss of fertilizer nitrogen.