This hydroponics experiment studied the differences in use of different forms of nitrogen (N) by starved rice crop (Oryza sativa L. ssp. Japonica cv. Wuyunjing 7 #). Re-supply of N stimulated growth of shoot but decreased biomass accumulation of roots, particularly by the single form of ammonium. In comparison to either ammonium or nitrate alone, mixture sup ply of the two forms of N increased total N uptake and translocation of N to shoot as well as activation of glutamine synthetase in the roots and nitrate reductase in the leaves. Concentration of total chlorophyll, particularly chlorophyll a in the ammonium supplied leaves was significantly higher than that nitrate supplied leaves. It suggests that balanced supply of both ammonium and nitrate through rational management of water and fertilization could improve both uptake and use efficiency of N by rice crop.