Abstract: Sixteen lignanoids were isolated from an aqueous extract of the commonly used Chinese traditional medicine Dangshen, the dried roots of Codonopsis pilosula, by using a combination of various chromatographic techniques, including silica gel, macroporous adsorbent resin, MCI resin, sephadex LH-20, and reversed phase semi-preparative HPLC. On the basis of spectral data analysis, their structures were elucidated and identified as (-)-(7R, 7'R, 8R, 8'S)-4, 4'-dihydroxy-3, 3', 5, 5', 7-pentamethoxy-2, 7'-cyclolignane (1), (-)-(7R, 8S)-dihydrodehydrodiconiferyl alcohol 4-O-β-D-glucopyranosyl-(1"'→2")-β-D-glucopyranoside (2), (-)-(7R, 8S)-dihydrodehydrodiconiferyl alcohol (3), (+)-(7S, 8R)-dehydrodiconiferyl alcohol (4), (+)-balanophonin (5), (+)-demethoxypinoresinol (6), (+)-pinoresinol (7), (+)-epipinoresinol (8), (-)-syringaresinol (9), (-)-medioresinol (10), (-)-lariciresinol (11), (-)-secoisolariciresinol (12), (-)-ent-isolariciresinol (13), (+)-(7S, 8S)-3-methoxy-3', 7-expoxy-8, 4'-neolignan-4, 9, 9'-triol (14), (+)-(7S, 8R)-3', 4-dihydroxy-3-methoxy-8, 4'-neolignan (15), and (-)-(7R, 8R)-3', 4-dihydroxy-3-methoxy-8, 4'-neolignan (16). All these compounds were isolated from C. pilosula for the first time, while compound 1 is a new natural product of 2, 7'-cyclolignan and 2 is a new 4', 7-epoxy-8, 3'-neolignan diglucoside. Compound 12 showed activity against Fe²⁺-cysteine induced rat liver microsomal lipid peroxidation with an inhibition ratio of (63.4±8.3)% at 1×10^-5 mol·L^-1.