The present investigation was conducted during 2014 and 2015 seasons to study the influence of foliar sprays with urea and yeast extract on vegetative and floral buds , leaf ammonium, fruit set, yield and fruit quality of 35- years old Washington navel orange trees on sour orange rootstock. Results revealed that a combination of urea plus yeast on Jan.,15, achieved the highest number of vegetative buds per branch and produced significantly the highest number of fruit set / branch  and achieving an increase in fruit number per tree, average fruit weights and fruit yield compared with other treatments. Single foliar application of urea in mid-January, significantly increased leaf ammonium concentrations and the total number of inflorescences (leafy had more flowers, one or two flowers) and leafless inflorescences. Trees sprayed with urea plus yeast on Feb., 15 and these sprayed with urea on Feb. , 15 have improved fruit size. Moreover, spraying trees with the two compounds, in mid-Jan. and mid-Feb. increased fruit and pulp weights, whereas , those sprayed with a mixture of urea plus yeast extract in mid-Jan. or urea in mid-Feb., produced fruits with significantly higher juice percent  and almost improved chemical fruit properties. Fruit nitrate and nitrite contents were in permitted limits due to foliar urea and yeast application. In addition, urea plus yeast extract, in mid-January and mid-February resulted in fruits having the lowest contents of nitrate and nitrite and similarly as the control.