Abstract: Plant exposed to salinity stress exhibit changes in their physiology and metabolism. In general salinity reduces water availability and causes nutritional imbalance in plants. Since there is no enough information about effect of salinity stress on activity of enzymes involved in nitrogen and phosphorous metabolism we studied the effects of different levels of salinity (0, 50, 100, 150 and 200 mM NaCl) on nitrate reductase, acid phosphatase and alkaline phosphatase activity as well as nitrate and phosphate uptake and total nitrogen content in leaves of canola, so a hydroponically experiment was conducted. Canola seeds were sown in an experimental green house under non-saline conditions. After two month, healthy plants were selected for hydroponic culture in Hoagland's nutrient solution supplemented with NaCl. The plants were cultured in plastic pots filled up with perlite and then were put in green house. The plants were watered with fresh nutrient solution made every week. Leaf samples were clipped 0, 7, 14, 21, 30 and 45 days after exposure to salinity stress in order to nitrate reductase, acid phosphatase and alkaline phosphatase assay, measurement of nitrate uptake, phosphate uptake and total nitrogen content. The results showed that nitrate reductase activity was increased in treated plants with 100 mM NaCl, in contrast it was decreased gradually in plants that were exposure to 150 and 200 mM NaCl, in comparison with controls. Decrease of nitrate reductase activity due to salinity stress and nitrate uptake and follow them total nitrogen content were occurred at the same time. Reduction in nitrate reductase activity, nitrate content and total nitrogen content because of high salinity levels may be a physiological response in order to decrease in growth and extra biomass in canola. However, it was observed that salinity stress caused an increase in both acid phosphatase and alkaline phosphatase activity. We monitored phosphate levels in leaves and found that phosphate levels decreased significantly under salinity stress. These results suggest that the induction of acid phosphatase and alkaline phosphatase under salt stress may be due to a phosphorous deficiency.