An activity-directed fractionation and purification process was used to identify the acetylcholinesterase inhibitory-active components of Rhodiola rosea L. (RR). Dried rhizome of RR was extracted with boiled ethanol. After removal of tannins, the extract was separated into chloroform, ethyl acetate, n-butanol and water fractions. Among these, chloroform and n-butanol fractions showed stronger activity by bioassay for anti-cholinesterase activity than did ethyl acetate and water fractions. The chloroform fraction was then subjected to separation and purification using silica gel column chromatography and Sephadex LH-20 chromatography. One compound, showing strong anti-cholinesterase activity, was identified by spectral methods (NMR, UV and MS) and by comparison with authentic samples. It proved to be hydroquinone.