The present study was carried out during 2007 and 2008 on 15 years old Washington navel orange trees (C. sinensis Osbeck) grafted on sour orange (C. aurantium L.) rootstocks. Trees were grown under north delta conditions. The results could be summarized in the following points: 1) The trees which sprayed with 100 g amcotone /100 L+ 20 ppm (GA₃) gave the highest initial and final fruit set % and the lowest (June drop% and preharvest drop%) followed by the trees which sprayed with 50 g  amcotone /100 L+ 20 ppm (GA₃) which obtained the second order in this regard in both studied seasons.        Also, there are no significant effects on number sprayed doses in this respect. 2) The trees which sprayed with 100 g amcotone /100 L+ 20 ppm (GA₃) gave the highest {fruits number and yield (kg) /tree} followed by the trees which sprayed with 50 g amcotone /100 L+ 20 ppm (GA₃) which possessed the second order in this regard in both seasons. Also, the trees which sprayed with three doses (mid-March, late April and the beginning of August) obtained the highest {fruits number and yield (kg) /tree}. 3) Fruit shape (H/D ratio) was the highest in trees which sprayed with100 g amcotone /100 L+ 20 ppm (GA₃) followed by trees which sprayed with 100 g amcotone /100 L+ 15 ppm (GA₃) with  insignificant effect of  three treatments. Whereas, non- significant effects of the number of doses . 4) Physical properties of fruits under this study as { fruit weight (g), fruit size (cm³) and fruit  juice weight (g) } the highest values obtained in  trees which sprayed with100 g amcotone /100 L+ 20 ppm (GA₃) followed by 50 g amcotone /100 L+ 20 ppm (GA₃).Moreover, trees which sprayed with three doses (mid-March, late April and the beginning of August) gave the highest values in this respect. 5) Regarding to the chemical properties of fruits which studied as ( T.S.S. %, total acidity % and Vitamin C mg/100 ml juice) the treatments which sprayed with100 g amcotone/100 L+ 20 ppm (GA₃) gave the highest values followed by the trees which sprayed with 50 g amcotone /100 L+ 20 ppm (GA₃) . Also, the trees which sprayed with three doses (mid-March, late April and the beginning of August) gave the highest values in this respect . 6) Trees which sprayed with Amcotone/100L+20 ppm GA3 treatment gave the highest values of T.S.S. /acid ratio with insignificant effect when compared with other treatments under this study. Moreover, trees which sprayed with three doses (mid-March, late April and the beginning of August) gave the highest T.S.S. / acid ratio.  The recommendations:     It could be recommended that spraying “Washington" navel orange trees with100 g amcotone /100 L+ 20 ppm (GA₃) three times at (mid-March, late April and the beginning of August) gave the highest values of initial and final fruit set %, decrease of June and preharvest drop %, increase of yield as fruit number and weight (kg) /tree, improvement fruit physical and chemical properties as {fruit weight (g) and size (cm³) and fruit juice weight (g),TSS% , total acidity % ,Vitamin C. and TSS/Acid ratio }.