The objective of this study was to investigate the effect of irradiation with ultraviolet-A (UV-A) on berry growth, the total soluble solids and titratable acidity of the juice, and anthocyanin contents of berry skins in 'Gros Colman' (Vitis vinifera) and 'Pione' (V.labruscana × V.vinifera) grapes. Clusters of mature 'Gros colman' and 'Pione' vines grown in glass or plastic film houses were irradiated with UV-A lamp in the daytime for 10 and 4 weeks during maturation, respectively. In 'Gros Colman' grapes, irradiation with UV-A markedly increased anthocyanin content in berry skins with the days after irradiation, and anthocyanin level in the skin of clusters irradiated with UV-A was four times that of control clusters at four weeks after treatment. At harvest, berries from exposed-side of UV-A irradiated clusters had the highest anthocyanin in the skin followed in the skill followed in descending order by exposed-side of non-irradiated clusters (control), and non-exposed-side of control and UV-A irradiated clusters. By contrast, anthocyanin content in the skin of 'Pione' grapes was not affected by irradiation with UV-A throughout the experiment. In both cultivars, no significant difference in either berry growth, the contents of total soluble solids or titratable acidity of the juice were observed among the treatments. Based on the results, the relationship between coloration og grape berries and UV-A irradiation during maturation is discussed.