A new lignan, actaealactone (1), and a new phenylpropanoid ester derivative, cimicifugic acid G (2), together with 15 known polyphenols, protocatechuic acid, protocatechualdehyde, p-coumaric acid, caffeic acid, methyl caffeate, ferulic acid, ferulate-1-methyl ester, isoferulic acid, 1-isoferuloyl-beta-d-glucopyranoside, fukinolic acid, and cimicifugic acids A, B, and D-F, were isolated from an extract of the rhizomes and roots of black cohosh (Actaea racemosa). The structures of the new compounds were determined on the basis of NMR spectroscopic analysis. Compounds 1 and 2 displayed antioxidant activity in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free-radical assay with IC(50) values of 26 and 37 microM, respectively. Other antioxidants identified from A. racemosa include cimicifugic acid A (3), cimicifugic acid B (4), and fukinolic acid (5). Compounds 1 and 2 also exhibited a small stimulating effect on the growth of MCF-7 breast cancer cell proliferation 1.24-fold (14 microM) and 1.14-fold (10 microM), respectively, compared to untreated cells.