The effect of picking dates on fruit set, dropping and nutrient change of Washington navel orange were studied during 2009/2010 and 2010/2011 seasons. It is an evident decrease in N, P and K contents in leaves and juice was obtained with delayed harvest date. Activity of pectin methyl esterase and polygalacturonase (PGU) enzymes in fruit peduncles was increased by delayed picking dates. This was related to increasing pre-harvest fruit drop percentage. Delaying time of fruit harvest increased gibberellic acid and indole acetic acid (IAA) and decreased abscisic acid in the leaves. Regarding successive season parameters, delaying harvest date delayed the flowering starting date and full bloom date and increased vegetative bud percentage and decreased flower bud percentage. Moreover, a decrease in fruit set in the following season was also noticed. The data also, revealed that content and endogens hormone of Washington navel orange trees that fruit dropping significantly increased with delaying the date of picking since, the earlier data gave a lower dropping than the other dates.