Cytotoxic bioassay-guided fractionation of methanol extract of Angelicae Sinensis Radix led to the isolation of a new dimeric Z-ligustilide, named neodiligustilide (1), together with three known compounds, Z-ligustilide (2), 11(S),16(R)-dihydroxy-octadeca-9Z, 17-dien-12,14-diyn-1-yl acetate (3), and 3(R),8(S)-falcarindiol (4). Among them, 2 showed the strongest cytotoxicity against L1210 and K562 cell lines with IC50 values of 2.27 +/- 0.10 and 4.78 +/- 0.18 microM, respectively, while 1 showed moderate cytotoxicity with IC50 values of 5.45 +/- 0.19 and 9.87 +/- 0.14 microM. Two polyacetylenes, 3 and 4, showed cytotoxicity only against L1210 cell line with IC50 values of 2.60 +/- 0.90 and 2.87 +/- 0.49 microM, respectively.