Acetylcholinesterase(AChE) inhibitors are one of the major classes of drugs use for the treatment of symptoms of neurodegenerative disease like Alzheimer's disease (AD), because they can increase the acetylcholine level in the brain. For the purpose of searching AChE inhibitors from natural resources, sixteen Thai medicinal plant extracts from Annonaceae and Myrtaceae families were screened for their AChE inhibitory activity using Ellman's colorimetric method in 96-welled microplates. Of these, the crude methanolic extract from stem of Baeckea frutescens L. belonging to Myrtaceae family exhibited the most potent activity with the percentage of AChE inhibitory activity (%IA) 92.14%. The wood extracts of Rauwenhoffia siamensis Scheff, Melaleuca quinquenervia (Cav.) S.T.Blake and Rhodomyrtus tomentosa (Aiton) Hassk. exhibited good enzyme inhibitory activity with %IA of 65.65, 65.22 and 64.59%, respectively whereas the stem extract of Annona squamosa L. and the leaf extract of Uvaria grandiflora Roxb. ex Hornem showed moderate activity with %IA of 51.30 and 55.38%, respectively. Therefore, Baeckea frutescens L. is an important target for further investigation on AChE inhibitory activity