The role of UV radiation in the accumulation of anthocyanin in 'Gros Colman' (Vitis vinifera L.), a light-sensitive cultivar, was examined by using berry sections prepared from the softened green berries at veraison. The sections were exposed to diffuse sunlight under covering materials such as glass plate, polyolefin film (PO), poly vinyl chloride film (PVC), UV-proof PVC, ethylenetetrafluoroethylene (ETFE), polycarbonate resin plate (PC), fiber-reinforced acrylic resin plate (FRA) for 72 hr. The accumulation of anthocyanin in the berry skins under diffuse sunlight was greatly reduced with the covering materials which prevent the penetration of UV light. Artificial irradiation with an UV lamp (peak wavelength: 352 nm) greatly promoted the accumulation of anthocyanin. With increasing light intensity in the UV-A region (320-400 nm) up to 0.4 W·m^-2, the anthocyanin content markedly increased, reached a plateau and then levelled off at 2.3 W·m^-2. Increasing the intensity of white light up to 8.5 W·m^-2 induced a gradual accumulation of anthocyanin. When UV irradiation was combined with white light at about 4.1 W·m^-2, the accumulation of anthocyanin was further enhanced. These results suggest that UV light is involved in the accumulation of anthocyanin in 'Gros Colman' grapes. Hence, UV permeability of covering materials in the protected culture should be considered.