In the two seasons of 2013/2014 and 2014/2015, 10 years old Washington navel orange trees (Citrus sinenses), on sour orange rootstock (Citrus aurantium L.), received ascorbic acid (AA) spry at 0 (control), 50, 100, 150, 200 ppm on three physiological stages: 1- at the beginning of flowering; 2- at full bloom; 3- at fruitlet diameter of 0.5-1.0 cm. All experimental trees received with about 7 liters of the spray solution at each spray time. The main goal of this study was to pilot AA effects on orange trees and to determine the most effective concentration. The data reveal that, increasing AA concentration enhanced mixed flower bud and bud opening percentages as well as total number of inflorescences, number of leafy inflorescences as well as total number of solitary flowers per twig in both seasons. The uppermost AA concentration (200 ppm) significantly increased number of fruits per tree since it reached 195.83 and 223.25 fruits / tree in the 1^st and 2^nd  seasons, respectively compared with 56.17 and 61.78 fruits / tree, respectively with the control. The yield per tree recorded 41.11 and 48.23 kg in the 1^st and 2^nd seasons, respectively with AA 200 ppm against only 14.73 and 16.01 kg, respectively for the control. In addition, the higher AA concentrations significantly increased IAA concentration in mature leaves, flowers and fruitlets.