This investigation was conducted in (2012 and 2013) seasons on 14 years old Valencia and Washington navel orange trees(Citrus sinensis L.) on sour orange (Citrus aurantium L.) rootstocks and spaced at 5 × 5 m in a private orchard. Its aim to study the effect of foliar spraying with seaweed extract at 200, 250 and 300 cm /100 liter in 2 stages (before flowering and after initial fruit set).        Foliar spraying with seaweeds extract on Valencia and Washington navel orange trees were significantly increased almost studied characters. The tested data of fruit set, yield, fruit quality and leaf chemical composition were max - in Washington navel orange trees compared to Valencia orange trees, where seaweeds extract gave maximized in Washington navel orange trees than in Valencia orange trees.         Trees sprayed with it gained that the longest shoot length as compared with untreated control trees. The largest leaf surface area/ area was recorded for trees that sprayed with seaweeds extract in both study seasons. Spraying seaweeds extract (300 / 100 liter which added before flowering) significantly affected initial fruit set % in both study seasons. Treat. (7) sprayed trees gained the highest initial fruit set percentage, followed by Treat. (4) compared with control trees.       Trees sprayed with seaweeds extract (300 cm / 100 liter) after initial fruit set led to reduce June drop % in both seasons than untreated ones. Tree yield (fruits number and kg/ tree) were significantly increased as compared to the control treatment.          Data revealed that fruit weight, fruit L/D ratio, T.S.S, T.S.S /acid ratio and vitamin C were significantly increased by foliar spraying with seaweeds extract associated with increasing concentration, where the highest values were obtained from (Treat. 7) followed by (Treat. 4) in both seasons compared to control.     In contract, total acidity was reduced with all treatments compared to control in both seasons.          In addition, Treat. (7) gave significant increment of leaf (mineral content) as N, P, K, Ca, Mg, Fe, Zn, and Mn followed by Treat. (4) in both seasons compared to control.         Also, data indicated that leaf content of chlorophyll (a & b) and carotenoids were increased when applied 300 cm seaweeds extract/ 100 liter after initial fruit set fallowed by the same concentration before flowering in both seasons compared to the control trees.        Generally, it could be concluded that applying seaweeds extract to Valencia and Washington navel orange trees at 200, 250 and 300 cm /100 liter in 2 stages/ season (before flowering and after initial fruit set) enhanced shoot length and leaf surface area and increased initial fruit set %, increased yield/ tree, improved fruit quality, increased leaf mineral content and decreased June drop comparing with control treatment. While 300 cm seaweeds extract/ 100 liter after initial fruit set gave the best net profit.