For the development of a new antidementia functional food or alternative drug using agricultural products,Job's tears (Coix lachrymajobi L.), which shows high acetylcholinesterase (AChE) inhibitory activity (55.1%) was selectedand the extraction conditions of AChE inhibitor were optimized. AChE inhibitor of Job's tears was maximally extractedwhen it was treated with 60% methanol at 40℃ for 6h. The AChE inhibitor of the methanol extracts was partially purifiedby systematic solvent extraction, thin layer chromatography, silica gel chromatography and reverse-phase HPLC and thepartial purified AChE inhibitor with inhibitory activity (IC50) of 0.608㎍ was obtained. The partial purified AChE inhibitorwas soluble in methanol and hexane, and insoluble in water. Its maximum absorption spectra was 230㎚ and also it was sta-ble in the range of 30℃ and 70℃ and pH 4.0-8.0 for 1h.