A FIELD experiment was carried out at the Experimental Farm of the Faculty of Agric., El-Mansoura Univ. during season 2015, arranged in split block design with 3 replicates to evaluate the effect of 3 rates of NPK treatments (50, 100 and 150 % from recommended dose) as main plots and 4 levels of sodium selenite in a foliar way (0, 10, 20 and 30 mg kg-1) as sub plots. Results indicated that NPK fertilization up to 100 % under study significantly increased the average values of chlorophyll, fresh and dry weight, and total content of N, P and K as well as soluble and insoluble oxalate concentrations in spinach leaves as compared to the untreated plants. More addition of sodium selenite foliar application of sodium selenite at the lowest rates of 10 and 20 mg L-1 significantly increased the aforementioned traits while at the highest rate (30 mg L-1) 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 in leaves as well as the activity of nitrate reductase enzyme were significantly increased with the level of sodium selenite increasing. Such effect was realized under all the forms of NPK-fertilizers. An adverse effect happened for the values of nitrate and nitrite accumulation in spinach leaves. It decreased sharply and significantly with increasing selenite level under all the investigated treatments. Obtained results proved that the foliar application of sodium selenite at the lowest levels (10 and 20 mg L-1) in combination with soil application of combined with NPK fertilization up to 100% is considered to be the most suitable treatment for all previous traits.