Abstract: This paper is to identify the anti-oxidative effect in vitro of the birch leaf flavonoids and their preventive effects on HUVEC cells from oxidative damages. Experiments are performed to determine the capabilities of the birch leaf flavonoids to eliminate the DPPH radicals, hydroxyl radicals and ABTS radicals, and their reductive activity as well as the cellular SOD, GSH-PX activities, and T-AOC were measured in order to prove that the birch leaf flavonoids are capable of resisting the radicals in vitro and preventing the cellular damages. Results demonstrated the birch leaf flavonoids ( 0.20 mg/m L) could scavenge the DPPH radicals by 86.89%, ABTS radical by 96.26% at 0.18 mg/m L, and the hydroxyl radicals fall by 50.50% in presence of 1.9 mg/m L flavonoids. The cellular SOD, GSH-PX and T-AOC were significantly enhanced by the 10 μg/m L flavonoids ( p < 0.01) . It's concluded that the birch leaf flavonoids markedly scavenge ( free) radicals and prevent cells from oxidative damages.