This study was carried out during two successive seasons, 2012 and 2013 in a private orchard in Barshom vallage located at El-Kalubia Governorate Egypt. Washington Navel Orange trees (Citrus Sinensis) budded on sour orange rootstock (Citrus aurantium, L.) were 7-years-old and planted at 5 x 5 meters under basin irrigation system. This investigation aimed to study the effect of selenium (Se) levels (0, 20, 40, 80 and 160 ppm) as foliar spray on growth, yield, fruit quality, leaf mineral content and enzymes activity of Washington Navel orange trees. The obtained data showed that, selenium had a significant promotive effect on growth, yield, fruit quality, leaf mineral content and enzymes activity of Washington Navel orange trees. Results indicated that treatment of Se at 40 ppm gave the highest significant results, whereas, treatment 160 ppm gave the highest fruit selenium content.