Objective: To investigate the material base of Yigan San

a Chinese herbal formula for Alzheimer's disease

and to provide theoretical foundation for the explanation of pharmacological mechanism. Method: The chemical constituents were isolated and identified by various chromatographic and spectral methods. Result: Fifteen compounds were isolated and identified as cadambine(1)

rhynchophyline(2)

liquiritin(3)

liquiritigenin(4)

isoliquiritin(5)

isoliquiritgenin(6)

saikochromoside A(7)

wogonin-7-O-glucuronide(8)

ononin(9)

tetrahydroxymethoxychalcone(10)

quercetin(11)

kaempferol(12)

senkyunolide I(13)

senkyunolide H(14)

and ferulic acid(15)

respectively. Conclusion: All these compounds were isolated from the active fraction of Yigan San for the first time.