The objective of the present study was to investigate the pathological changes of the acute toxicity of Malathion as organophosphorus insecticide in wild pigeons (Rock dove). Liver enzyme Alanine Transaminase (ALT) in the serum of treated pigeons was measured. The maximum tolerated dose of malathion was 3.525mg / kg B.W. However, when the maximum tolerated dose of the malathion was given to group A, two out of eight pigeons died within two hours after treatment .The insecticide caused clinical signs appeared within two hours before death, they included salivation, lacrimation , gasping, frequent defecation, drooping of wings, tremors, convulsion and recumbancy. Also the histopathological changes of the acute toxicity of present study included vacculation of nerve fibers in the spinal cord and sciatic nerve, meningitis associated with lymphocytic infiltration in the brain, myocardial fibrosis, aggregation of lymphocytes and hepatic septal fibrosis. Cortical fibrosis with inflammatory cells, regenerating renal cortical tubules and dilated cortical tubules were also seen. Compared to control values the exposure to insecticide caused increase of the ALT level in the serum for treated pigeons, and this increment was significant. In conclusion Malathion insecticide administered orally at maximum tolerated dose induced clinical signs of poisoning, pathological changes in different organs of pigeons and increased the ALT value.