21H24O6。;Objective: To isolate and purify active component from Arctii Fructus and identify and characterize. Methods: The crude product was separated from Arctii Fructus by alcohol extraction and acid hydrolysis. Using recrystallization its structure was method, colorless prismatic crystal was obtained. The composition and molecular structure were characterized by UV, FTIR, MS, 1H-NMR, 13C-NMR, and X-ray analyses. Results: The extracting rate of the crystal gained from the powder of Arctii Fructus was 4.46%. Both color reactions and spectral analyses indicated that the compound was lignan. Conclusion: The active component is characterized as (3R, 4R)-4-[(3,4-dimethoxyphenyl) methyl] dihydro-3-[(4-hydroxy-3-methoxy phenyl) methyl]-2(3H)-furanone (arctigenin, ARC-G) and the molecular formula is C21H24O6."/>