Abstract: The study analyze the effect of pesticide-acetamiprid on protein content and carbohydrate content of liver, brain and gill tissues of Oreochromis mossambicus. Acetamiprid is an neonicotinoid pesticide and is used by the farmers to protect their crops. Pesticides may enter water bodies as a result of spray drift and leaching from the soil in concentrations, which may exert adverse effects on fish populations. Lethal concentration (LC50) of acetamiprid for O. mossambicus has been calculated by probit analysis and recorded as 5.99 ppm at 96 h. Chronic exposure shows decreased protein and carbohydrate content in liver, brain and gill tissues during all the exposure periods when compared with the control. This significant decrease in protein and carbohydrate content was observed due to toxic effect of acetamiprid. Long term exposure of organisms to pesticides means a continuous health hazard for the fish population and it is on high risk by consuming these toxicated fishes.