Enzymes are biocatalysts. They catalyse reactions by stabilizing the transition state and are highly specific for reactions that they catalyse as well as their substrates. Enzymes usually catalyse only one or small number of similar reactions. The most important part of the enzyme is their active site where reactions take place. Acetylcholinesterase (AChE) is an enzyme that belongs to the hydrolases group and catalyses the hydrolysis of the acetylcholine neurotransmitter to acetate and choline. In this study AChE from the electrophores of electric eel (type V-S) was used as a source of the enzyme and acetylthiocholine iodide (ATChI) was used as a substrate while α-terpinolene was tested for AChE inhibitory activity. Inhibition of acetylcholinesterase has a crucial role in the treatment of Alzheimer's dementia. The aim of this study was to examine the ability of α-terpinolene to inhibit AChE and to determine the type of inhibition. After reviewing the results using Lineweaver-Burk, Eadie-Hofstee, Hanes-Wolf and Eisenthal – Cornish-Bowden plots as well as calculating the inhibition percentage it was concluded that α-terpinolene shows ability to inhibit the AChE in concentration dependant manner. Maximum percentage of AChE inhibition, 91,8 %, was achieved at α-terpinolene concentration of 0,0227 mg mL-1. It was, also, concluded that α-terpinolene exhibits a mixed type inhibition and appropriate kinetic parameters were determined i.e. KM, Vmax, KMapp, Vmaxapp, KI i K'I.