Fruit weight, juice quality, fruit skin color, the concentration of total anthocyanin and individual anthocyanins in fruit skin, and the percentage of individual anthocyanins in'Reliance'grape (Vitis hybrid) were investigated after cluster-thinning treatments were imposed. Cluster-thinning treatments were 60 (control), 40, and 20 clusters per vine, and applied when the berries were 2-3 mm in diameter. Twenty clusters per vine produced fruits of the best weight, juice quality, and color among three cluster-thinning treatments. Fruit cluster thinning decreased vine yield significantly, following a quadratic relationship. Juice soluble solids concentration (SSC) was increased significantly by cluster thinning treatments. Individual berries were heavier with 20 clusters per vine than with 60. Juice pH was not affected by cluster thinning. Juice titratable acid concentration was lower at 20 clusters per vine than with 60 clusters per vine. Twenty clusters per vine produced fruits darker and less yellow than 60 clusters per vine. Fruit red pigmentation was increased quadra~ cally by cluster thinning. Total anthocyanin concentration in berry skin was increased linearly by cluster thinning. The concentration of individual anthocyanins, including cyanidin-3-glucoside, peonidin-3-glucoside, and acylated cyanidin derivative, was increased linearly by cluster thinning.