Objective: To investigate and screen the active compounds of Huanglianjiedu decoction（HLJD） for senile dementia. Method: Inhibition on acetylcholinesterase and antioxidant activity by HLJD was studied with ultraviolet spectrometry. The single herbs and the major compounds of HLJD were also determined and compared by a rapid and effective acetylcholinesterase inhibition assay and antioxidant assay. Result: The formula HLJD had a better antioxidant activity than single herbs except for Radix Scutellaria which is rich in polyphenolic compounds. The most active conpounds was baicalin （ IC50 = 12. 06 μg·mL -1 ）. The results also indicate that the most active herbs and compounds for AChE inhibition were Coptidis Rhizoma （IC50 = 18. 89 μg·mL -1） and berberine （ IC50 = 9. 52 μg·mL -1）; Radix Scutellariae

Fructus Gardenia as well as the major compounds of them showed no or lower inhibitory activity. Conclusion: It can be concluded that alkaloid compounds in HLJD contribute to the inhibitory activity for acetylcholinesterase and flavanoids compounds contribute to the antioxidant activity.