Abstract: The effect of UV-B irradiation on fruit quality and flavonol accumulation of postharvest grape berry ( Vitis Vinifera L.Cabernet Saubignon) was studied. The results showed that the content of titratable acid, total phenol, total flavonoid and total flavonol was significantly enhanced by proper UV-B irradiation without affecting the firmness and the browning index of grape stems, and the degradation of soluble solids and vitamin C was significantly slowed down, which indicated that UV-B irradiation improved fruit quality of postharvest grape berry, but the effect of UV-B irradiation was irradiation-dose-dependent and incubation-time-dependent. The optimum condition of UV-B irradiation in terms of improved fruit quality and increased flavonol content was determined to be 150 μW/cm2 and 2 h.