Thompson seedless is one of the most important table grape cultivars grown in Egypt. In recent years, the H4 strain has become widely cultivated because of its high yield. However, this strain produces clusters with high compactness and small berries, thus negatively affecting the quality. A field experiment was carried out during the two successive seasons of 2018 and 2019 on Five years-old Thompson seedless cultivar (H4 strain) grapevines grafted onto freedom rootstock. The investigation was designed to shed light on the effect of 10, 20, and 30 ppm GA3 for thinning at the full bloom plus 20, 30, and 40 ppm GA3 for sizing after fruit set on reducing cluster compactness and improving quality. Data indicated that the total chlorophyll content decreases when the GA3 concentration increases, while GA3 spraying for thinning and sizing treatments was higher than others for thinning only concerning pruning weight. The results also showed that the optimum GA3 dose was 20 ppm at the full bloom for thinning, then spraying 30 ppm GA3 for sizing (T6) to get high cluster weight, yield per vine, and low compactness, as well as highest TSS, TSS/acid ratio, and lowest acidity good quality. Overall, spraying 20 ppm GA3 at the full bloom and 30 ppm GA3 for sizing could be recommended to get the most suitable yield and quality.