This investigation was undertaken during seasons of 2005 and 2006 to study the effect of potassium and magnesium fertilization each alone or in combination on vine vigour, vegetative growth and leaf mineral content of Thompson Seedless grapevines.                 Potassium was applied to the soil as potassium sulphate at  75, 150 and 225 g/vine. Also, magnesium was applied as magnesium sulphate at 0, 30 and 60 g/vine. Since, potassium and magnesium fertilization were applied in two equal doses one before bud burst and the second after fruit set.                 From this study it is clear that, potassium fertilization at 150 g with 30 g magnesium sulphate increased both internodes length, thickness and trunk growth than the other treatments used or the control. Furthermore, potassium fertilization at 225 g with magnesium sulphate at 60 g per vine gave a higher leaf area than the other level of fertilization. The data also reveal that both potassium and magnesium fertilization increased the values of nitrogen, potassium and magnesium in leaf petiole, but reduced the level of phosphorus and calcium content in leaf petiole than the control.