In this study, the effect of soluble extracts of five plants on the inhibition activity of acetylcholinesterase (AChE: E.C.22.214.171.124) enzyme were investigated. The results indicated that some of the plants achieved inhibition AChE which is an important enzyme for the nervous system of the human body. AChE catalyzes the hydrolysis of acetylcholine, a neurotransmitter substance which functions in certain parts of the nervous system. Ziziphora clinopodioides L., Chrysopthalmum montanum (DC.), Boiss. (Asteraceae), Melissa officinalis L. (Labiatae), Plantago (Plantaginaceae) lanceolata L. and Valeriana officinalis L. (Valerianaceae) plants are used for pharmacotherapeutic (cancer) aims by the people, in the east region of Turkey. In this study, the effect of soluble extracts of five plants on AChE activity was investigated in vitro. Cholinesterase activity was spectrophotometrically measured using acetylthiocholine iodide (AChI) as a substrate and dithiobis-nitrobenzoic acid (DTNB) as the coloring agent using different aliquots of the plant extracts. Ziziphora clinopodioides L. and Chrysopthalmum montanum were shown to have competitive inhibition on the erythrocyte, but Melissa officinalis L. and Plantago have shown noncompetitive inhibition effects on the erthrocyte. Melissa officinalis L. had shown non-competitive inhibition effects on the serum. The extracts of the five plants used in this study were found to inhibit AChE in the test at different concentrations. This study is the first one to show the relationships of erythrocyte and human serum AchE activity, in Labiatae family (Lamiaceae), Valeriana officinalis L. (Valerianaceae), Chrysophthalmum montanum, Ziziphora tenuior L., and lemon balm (Melissa officinalis).