Considering the crucial role of grape marketability in determining consumer preference and commercial success, this study was conducted to evaluate the effects of brassinosteroid (BR) application on quantitative fruit attributes of Vitis vinifera L. cv. Thompson Seedless. The experiment was performed through foliar spraying at the berry green-tip stage, with treatments consisting of different BR concentrations (0 as control, 0.5, 0.75, and 1.5 mg L⁻¹). The results revealed that BR application at 1.5 mg L⁻¹ exerted the most pronounced effect, leading to significant increases in cluster weight (≈43% higher than the control), berry number per cluster (over 31% increase), and single berry weight (more than 228% increase) at harvest. These substantial improvements highlight the synergistic role of BR in enhancing cell division, fruit development, and the regulation of growth-related metabolic pathways. The remarkable efficiency of BR at higher concentration appears to be associated with its ability to stimulate net photosynthesis, enhance protein biosynthesis, and modulate hormonal balance within the vine. Moreover, the concentration-dependent response of the studied traits confirms the pivotal role of BR dosage in activating morphogenetic and growth-promoting mechanisms. In conclusion, foliar application of brassinosteroid, particularly at 1.5 mg L⁻¹, can be considered a promising management tool to improve the quantitative yield attributes of Thompson Seedless grape, thereby contributing to enhanced fruit marketability and consumer acceptance.