The desert locust Schistocerca gregaria is a dangerous pest for several fields and orchard crops. Great attention has been paid to use botanicals for controlling this pest. The current investigation aimed to assess the disturbing effect of margosan-O^® (0.3% Azadirachtin) on the acetylcholinesterase (AchE)activity in haemolymph and fat bodies of S. gregaria. The penultimate (4^th) instar nymphs were treated, via the fresh food, with two concentrations (0.9 and 0.4%) of margosan-O^® and the activity of AchE was estimated in the last instar nymphs and newly emerged adults. The most important results could be shown as follows. In the present study, margosan-O^® caused a predominantenhancement of AchE activity in the haemolymph of last instar nymphs and adults, regardless of the concentration. Also, the enzyme activity was induced in fat bodies of nymphs and adults, with exception of the late-aged nymphs, nymphs. In these late-aged nymphs, the AchE activity was inhibited in the fat bodies (60.8 and 65.3% decrements, at the higher and lower margosan-O^® concentrations, respectively).