In order to study the objectives of this investigation; two pot experiments were conducted under green house conditions in The Faculty of Agric. Mansoura Univ. the experiment were conducted during the seasons of 2012-2013 and 2013-2014 to study the interaction effect among N-forms, Ca and Se application on some bio-chemical parameters of spinach plant. Thirty treatments were arranged in complete randomized block design with three replicates, which were the simple possible combination between two treatments of calcium (0 and 100 mg.L^-1), the three treatments of N-forms (ammonium sulphate, urea, and ammonium nitrate) at 60 kg N/fed. and the five levels of sodium selenite (0, 5, 10, 15 and 20 mg.L^-1). N-forms were added as soil addition, while calcium and sodium selenite levels were foliarly applied. The results showed that; foliar application of sodium selenite at the lowest rates of 5 and 10 mg.L^-1 combined with N-forms under study in the presence of calcium applied by foliar way significantly increased the average values of chlorophyll, fresh weight, and soluble and insoluble oxalate concentrations in spinach leaves as compared to the untreated plants. More addition of sodium selenite at the highest rates of 15 and 20 mg.L^-1 under the same conditions of N-forms and calcium applications significantly reduced the average values of all the previously mentioned traits.    Also, the results, indicated that the mean values of total phenolic compounds, Se accumulation as well as the activity of nitrate reductase enzyme were significantly increased with the level of sodium selenite was increasing. Such effect was realized under all the forms of N-fertilizers in the presence and absence of calcium addition. An adverse effect happened for the values of nitrate and nitrite accumulation in the leaves of spinach plant. It deacresed sharply and significantly as the level of Na₂SO₃ increased under all the investigated treatments.