This study was carried out during 2002 and 2003 seasons to investigate the effects of phenylalanine (at 100, 200 or 400 ppm), putrescine (at 200, 250 or 300 ppm) and spermidine (at 50, 100 or 150 ppm), at full bloom on yield and berry quality of Thompson Seedless grapevines. The vines were grown at vineyard of Fac. Agric., Suez CanalUniv., Ismailia, Egypt. In this respect, phenylalanine at 400ppm exhibited high yield per vine due to its effect on increasing berry weight. Contrary, pruning weight, total carbohydrates, nitrogen, potassium and total acidity were significantly decreased as concentration of the tested chemicals increased, while phosphorus content was not significantly affected. The increments of amino acids and berry volume were detected by spraying spermidine at 100 ppm. In addition, putrescine at 300ppm or phenylalanine at 400ppm recorded the highest weight of 100 berries, cluster length and width and soluble solids content. Therefore, phenylalanine at 400 ppm or putrescine at 300 ppm may be considered as the most effective treatments in increasing vine yield and improving berry quality.