Three new compounds, (7E)-2beta,3alpha-dihydroxy-megastigm-7-en-9-one (1), 3-[5,7-dihydroxy-2-(4-methoxyphenyl)-4-oxo-4H-chromen-8-yl]-4-methoxybenzoic acid (2), and 4'-O-methyl myricetin 3-O-(6-O-alpha-L-rhamnopyranosyl)-beta-D-glucopyranoside (3), were isolated from Ginkgo biloba, together with 27 known compounds. The structures of the new compounds were determined primarily from 1D- and 2D-NMR analysis. The 4-O-methylbenzoic acid structural feature at C-8 in 2 is encountered for the first time. The antioxidant activities of 29 compounds isolated from Ginkgo biloba were evaluated on intracellular reactive oxygen species in HL-60 cells. It was found that quercetin, kampferol, and tamarixetin had antioxidant activity that was approximately 3-fold greater than that of their respective glycosides and also approximately 3-fold greater than that of a standard ascorbic acid with an IC(50) at maximum effectiveness.