This investigation was undertaken during seasons of 2005 and 2006 to study the effect of potassium and magnesium as soil fertilization each alone or in combination on bud behavior, yield and berry quality of Thompson Seedless grapevines.                 Potassium was applied to the soil as potassium sulphate at three rates 75, 150 and 225 g/vine. Also, magnesium was applied as magnesium sulphate at 0, 30 and 60 g/vine. Since, the two fertilizers potassium and magnesium were applied in two equal doses before bud burst and after fruit set.                 This study indicated that, potassium sulphate at 150 g with magnesium sulphate at 60 g per vine gave a higher yield per vine and per feddan. Since, this treatment increased both cluster and berry weight during the two seasons. The data also reveal that, the higher level of potassium fertilization (150 or 225 g/vine) with magnesium sulphate at 60 g per vine increased both SSC and SSC/acid ratio in berry juice. Yet vines treated with 225 potassium sulphate and 60 g magnesium sulphate gave a higher bud burst and fertility.