THE present investigation was conducted during two successive seasons of 2012 and 2013 on Hollywood and Santarosa plum Cvs. (Prunus salicina). Trees were 10 years old and grown in a private farm at desert road in Menofia Governorate. CPPU at 5 or 10 ppm were sprayed three times (after one week, two weeks and three weeks of full bloom) on both plum cultivars. Results showed that spraying with 5 or 10 ppm CPPU after one week of full bloom recorded the highest values of fruit set, yield, fruit weight, size, length, diameter, firmness and acidity and the lowest values of fruit drop and TSS. Control recorded the lowest values of fruit set, yield, fruit weight, size, length, diameter, firmness and acidity and the highest values of fruit drop and TSS in both seasons for the two cultivars under study. So, the study recommend to spray 5 or 10 ppm of CPPU after one week of full bloom to increase fruit set, yield and to improve fruit characteristics.