To study the chemical constituents of the roots of Angelica sinensis.Silica gel column chromatography was used to separate the chemical constituents. Their structures were elucidated by chemical and spectral analysis (IR, MS, 1D and 2D NMR, etc.).Besides three known phthalide derivatives, one new dimeric phthalide derivative and a pair of epimer were isolated and their structures were identified as Z-3',8',3'a,7'a-tetrahydro-6,3',7,7'a-diligustilide-8'-one (1), Z,Z'-6,6',7,3'a-diligustilide (2) and the 8-epimer (3) of 2 on the basis of spectral data.Compound 1 is a new dimeric phthalide derivative, and compound 3 was first reported from radix Angelica