Neem is the common name given to the different species of large, evergreen, glabrous shady trees, grown in semi-arid regions of the world. In Pakistan and India the common neem tree, also popularly known as Margosa is Azadirachata indica A. Juss. Neem products isolated from the neem tree were nimbinin, nimbin and nimbidin. Siddiqui (1942) was the first scientist to isolate and purify the neem constituents of its extract. In the present study, effects of Cypermethrin and two crude ethanolic neem extract RB-a and RB-b on the activity of enzymes (GOT, GPT, LDH and cholinesterase) against the 3rd instar larvae of Aedes aegypti. Based on present study results, it was concluded that the neem extract RB-a and RB-b is a moderately toxic substance that shows the toxic effects and morality at high concentrations. Basically it is an IGR that does not kill the insect directly by its poisoning effect rather kill them by interfering the physiological activities. The research techniques and information are helpful for graduate and research students of Biological Sciences and Environmental toxicology.