Abstract: By using the method of nutrient solution culture, simulated water stress by PEG(6000) and inhibited aquaporin activity by HgCl2, we studied the effects of different nitrogen forms (NO3-, NH4+ and NO3 -/NH4+) and water stress on growth, water uptake and photosynthesis of rice seedlings. Under non-water stress, the biomass of rice plants was approximately 16.95% and 49.12% higher on treatment with nitrate and ammonium together than with ammonium or nitrate alone, respectively, and under water stress, the dry weight of rice plants was approximately 10.92% and 39.57% higher with nitrate and ammonium together than with the other two treatments. Under non-water stress, 3-hour water uptake per dry weight of rice plant was the highest with nitrate treatment alone, and with 0.5 mmol.L-1 HgCl2 closing the water channel (aquaporins), the reduction of water uptake with nitrate treatment alone, ammonium alone and nitrate and ammonium together was 9.6%, 20.7% and 16.0%, respectively. However, under water stress, the 3-hour water uptake per dry weight of rice plant declined significantly with nitrate treatment alone and was significantly lower than with both nitrate and ammonium together and ammonium alone. With 0.5 mmol.L-1 HgCl2 closing the water channel, the reduction in water uptake with nitrate treatment alone, ammonium alone and nitrate and ammonium together was 1.0%, 18.8% and 23.5%, respectively. Under non-water stress or water stress, rice plants with ammonium treatment alone had the highest net photosynthetic rate, stomatal conductance, transpiration rate and concentration of intercellular CO2. As compared with under nonwater stress, under water stress, all the photosynthetic characteristics decreased, except for concentration of intercellular CO2, with nitrate treatment alone. The results of HgCl2 inhibition show that aquaporin activity might be affected by a different nitrogen form of nutrition of rice seedlings.