During 2006 and 2007 on 15 years old Thompson Seedless grapevines sprayed dormant buds with three concentrations of hydrogen cyanamide at 2, 3 or 5% and (control) and three dates of applications (1, 7 and 14 Jan.). All hydrogen cyanamide treatments  increased yield generally. Meanwhile increased number of cluster, berry weight of 100 berries (g) and perry size. Total sugars and total soluble solids (TSS) with increasing hydrogen cyanamide concentrations. Whereas total acidity and chlorophyll was reduced, whereas early application increased with increasing hydrogen cyanamide (TSS) and total sugars, wherease total acidity was reduced. Moreover late hydrogen cyanamide application significantly increased the yield generally of Thompson Seedless grapevines compared to the control. Hydrogen cyanamide treatments significantly decreased total phenols, as compared with the control.