Two types of cholinesterase enzymes, electric eel AChE and horse serum BChE, were used whereas ATCI and BTCI were used as substrates, respectively. The enzyme inhibitory action was dine by means of Ellman's method. Briefly, 50 ml of 50 mM This-HCI buffer pH 8, 25 ml of 1.5 mM ATCI or BTCI, 125 ml of 3 mM DTNB and 2.5 ml of the extracted oils in This-HCI buffer containing 10% methanol were mixed orderly. Then, 25 ml of 0.25 U/ml AChE or 0.91 U/ml BChE was added and the reaction was spectrophotometrically followed for 2 min at 415 nm by a microplate reader (Bio-Rad Laboratories Ltd., Japan). In the csse of inhibitory activities evaluation of microemulsion, 25 ml of microemulsion containing 10% of the extracted oil was added instead of the experiments were done in triplicate. The slope of the plot of absorbance versus time was taken as the enzymatic reaction rate. The enzyme inhibitory activity (lnh) was calculated as 1-(Vs/Vb), in which Vs is the mean reaction rate in the presence of a certain concentration of the oils and Vb is the mean reaction rate in absence of the oils. IC50 values were statistically evaluated using the Graphpad/Prism program