Byline: Khurshid Anwar and A.R. Shakoori Abstract.- Toxicity of cypermethrin insecticide was evaluated in the liver of 16-day old chick embryo following administration of a single sub -lethal dose of cypermethrin into the eggs on day '0' of incubation. The biochemical analysis of the liver revealed that the activities of aspartate aminotransferase, alanine aminotransferase and lactate dehydrogenase were significantly increased. The activities of amylase, alkaline phosphatase and acid phosphatase remained unchanged. Besides that hepatic glucose, total protein, total lipids, cholesterol, urea, uric acid and RNA contents were found to decrease, while, glycogen and DNA contents were elevated. The hepatic soluble protein and free amino acids contents, however, remained unaltered. Cypermethrin-induced histopathological changes in liver included increased sinusoidal spaces in hepatic parenchyma, cytoplasmic vacuolations in hepatocytes, hepatocytic nuclear condensation, fatty degeneration, hydropic degeneration and necrosis of hepatocytes.