Two field experiments were carried out at Ras-Sudr Research Station, DesertResearchCenter, during 2002/2003 and 2003/2004 growing seasons, to study the effect of potassium fertilization on growth characters, yield and its components and chemical compositions of three fodder beet varieties. The results revealed that: 1- Significant differences were obtained between the three varieties under study in growth, yield, its components and chemical compositions. The polyaurea, D.L. variety attained the highest values in growth and yield characters. While, the lowest values were obtained from Gent balance variety. It could be concluded that the polyaurea, D.L. variety of fodder beet is more adapted under saline condition South Sinai. 2- Raising potassium concentration added as spraying or soil application caused gradually increasing in growth as well as forage yield characters . 3- The highest values of crude protein and carbohydrate as well as potassium contents in tops and roots were obtained by using polyaurea,D.L.variety and 72Kg.K₂O/fed. 4- N and K contents were higher in top than in root, they reached to maximum values by the interaction treatment of polyaurea,D.L.variety x 72Kg.K₂O/fed. 5- Crude protein and carbohydrate contents were higher in root than in top and reached to it highest values by the interaction treatment of polyaurea,D.L.variety x 72Kg.K₂O/fed.