Mung bean (Vigna radiata L.) is an increasingly important human food source, as well as a new functional agent, mainly due to its potent antioxidant activity. This study was conducted to determine antioxidant activity of fractions from mung bean seeds by measuring DPPH radical scavenging activity and to quantify the flavonoids by means of HPLC analysis. Vitexin and isovitexin were present in both ethanol and water extracts in highest amount. Flavonoids, vitexin and isovitexin were quantified from 195 germplasms of mung beans and their concentrations varied by 4.7 fold. Especially, the breeding line KM99004-4B-2 (Suwon28/KM94004), which has grown in Jeollanamdo Agricultural Research and Extension Services, showed the highest amount (15.88 mg/g) of total flavonoids. The vitexin portion was averaged $70.73{pm}1.38\%$. High positive correlation $(r=0.96^{***})$ between vitexin and isovitexin contents showed. However, the flavonoid content showed very low correlation with the 24 growth and ecological characteristics. Seed coats of mung beans had the highest flavonoid amount, showing $50~70$ times more than cotyledons. Flavonoid contents in the seed, the cotyledon, and the seed coat were decreased as the seed imbibition time increased.