Abstract : An experiment was undertaken to study the effect of sub lethal effect of phorate on the acetylcholinesterase production in the Indian Major Carp rohu Labeo rohita (Linn.). The fishes were exposed to sub-lethal concentration of phorate at a dose of 18.846 μg/l. On 10, 20 and 30 days of exposure of sub-lethal test concentration of phorate, the acetylcholinesterase level in the liver, muscle, gill and brain of the fishes were estimated.