Abstract: The effects of water stress on nitrogen forms, activities of some enzymes related to nitrogen metabolism and photosynthetic properties in rice were studied using a hydroponic experiment. Water stress was caused by adding PEG-6000 into the solution. Slight water stress ( PEG 5%, Water potential - 0.05 MPa ) has little effects on contents of amino acid nitrogen, soluble protein and activities of nitrate reductase ( NR ), glutamine synthetase ( GS ), glutamate synthase ( GOGAT ) and glutamate dehydrogenase (GDH)，and moreover the absorption and accumulation of nitrate nitrogen are stimulated. However, photosynthetic rate and dry matter accumulation are significantly inhibited. The dry matter accumulation change is significantly correlated with the regulation of photosynthetic rate more than that positive effect of resisting badness effect from environment. Therefore, photosynthetic rate has much more effect on dry matter accumulation than metabolism in vivo of rice. When PEG concentration 10 ％( Water Potential-0.15 MPa ), the concentrations of different nitrogen forms, some key enzymes of nitrogen metabolism and photosynthetic rate are significantly decreased. These effects on roots under the water stress are significantly larger than those on leaves. The above results indicate concentrations of different nitrogen forms and some key enzymes of nitrogen metabolism and photosynthetic rate are closely related to the intensity of water stress.