The effects of ammonium and nitrate as the nitrogen source on concentration of NO₃--N, NH₄+-N, amino acids, protein, carbohydrates and site of nitrogen assimilation were studied in Nerium oleander L. under NaC1 salinity. Plants were grown in semi automatic sand culture system in the green house. We distinguished different distribution of carbohydrates and amino acids by nitrogen source under salinity. Ammonium and amino acids concentration increased in roots of ammonium treatment by salinity whereas protein concentration decreased. The level of carbohydrates decreased in leaves and increased in roots by salinity in ammonium treatment. No significant change in level of amino acids and carbohydrates was observed in nitrate treatment due to salt stress. Based on concentration of NO₃--N, NH₄+-N in xylem sap, glutamine synthetase and nitrate reductase activity, nitrogen assimilation was mostly done in roots and leaves in ammonium and nitrate treatments respectively. The lower tolerance of ammonium fed plants than nitrate is mostly related to higher diversion of carbohydrates from structure production to roots for ammonium detoxification and osmotic adjustment in ammonium fed plants under salinity.