The effect of nitrate (NO3-) on rice (Oryza sativa L.) growth as well as N absorption and assimilation during different growth stages was examined using three typical rice cultivars. Dry weight, yield, N uptake, nitrate reductase activity (NRA) in leaves, and glutamine synthetase activity (GSA) in roots and leaves during their entire growth periods, as well as the kinetic parameters of ammonium (NH4+) uptake at the seedling stage, were measured with solution culture experiments. Results indicated that addition of NH4+-N and NO3--N at a ratio of 75:25 (NH4++NO3- treatment) when compared with that of NH4+-N alone (NH4+ treatment) increased the dry weight of ’Nanguang’ cultivar by 30% and ’Yunjing 38’ cultivar by 31%, and also increased their grain yield by 21% and 17%, respectively. For the four growth stages, the total N accumulation in plants increased by an average of 36% for ’Nanguang’ and 31% for ’Yunjing 38’, whereas the increasing effect of NO3- in the ’4007’ cultivar was only found at the seedling stage. In the NH4++NO3-treatment compared to the NH4+ treatment, NRA in the leaves increased by 2.09 folds, and GSA increased by 92% in the roots and 52% in the leaves of the three cultivars. NO3- supply increased the maximum uptake rate (Vmax) in the ’Nanguang’ and ’Yunjing 38’ cultivars, reflecting that the NO3- itself, not the increasing N concentration, increased the uptake rate of NH4+ by rice. There was no effect on the apparent Michaelis-Menten constant (Km) of the three cultivars. Thus, some replacement of NH4+ with NO3- could greatly improve the growth of rice plants, mainly on account of the increased uptake of NH4+ promoted by NO3-, and future studies should focus on the molecular mechanism of the increased uptake of NH4+ by NO3-. The effect of nitrate (NO3-) on rice (Oryza sativa L.) growth as well as N absorption and assimilation during different growth stages was examined using three typical rice cultivars. Dry weight, yield, N uptake, nitrate reductase activity (NRA) in leaves, and glutamine synthetase activity (GSA) in roots and leaves during their entire growth periods, as well as the kinetic parameters of ammonium (NH4 +) uptake at the seedling stage, were measured with solution culture experiments. -N and NO3 - N at a ratio of 75:25 (NH4 + + NO3- treatment) when compared with that of NH4 + -N alone (NH4 + treatment) increased the dry weight of ’Nanguang’ cultivar by 30% and ’Yunjing For the four growth stages, the total N accumulation in plants increased by an average of 36% for ’Nanguang’ and 31% for ’ Yunjing 38 ’, while the increasing effect of NO3-in the’ 4007 ’cultivar was only fou nd at the seedling stage. In the NH4 ++ NO3-treatment compared to the NH4 + treatment, NRA in the leaves increased by 2.09 folds, and GSA increased by 92% in the roots and 52% in the leaves of the three cultivars. NO3 That the supply of the maximum uptake rate (Vmax) in the ’Nanguang’ and ’Yunjing 38’ cultivars, reflecting that the NO3- itself, not the increasing N concentration, increased the uptake rate of NH4 + by rice. There was no effect on the Thus, some replacement of NH4 + with NO3- could greatly improve the growth of rice plants, primarily on account of the increased uptake of NH4 + promoted by NO3-, and future studies should focus on the molecular mechanism of the increased uptake of NH4 + by NO3-.