Acute toxicity (96 h LC50 – 0.5 ppm) of profenophos was evaluated in the freshwater fish Anabas testudineus fingerlings in static bioassay over a 96 –h exposure period using probit method. Histopathological investigations revealed various degrees of pathological lesions in intestine, muscle, liver and kidney. An apparent aberration in the histological architectures of the tissues has been observed in the vital organs of Anabas testudineus after 28 days of treatment with profenophos. Sloughing of mucosal lining, hypertrophy of intestinal epithelium were documented in the intestinal tissue. In the muscle tissues splitting of muscular fibres, vacuolar degeneration and atrophy of muscle bundles were conspicuous. Disintegration of hepatocyte cells boundaries, dilation of blood sinusoids, vacuolation and necrosis of hepatocytes were registered in the liver tissue of profenophos treated fish. Dilation of glomerular capillaries, shrinkage of glomerulus and hypertrophy of renal tubules were perceived in the kidney tissue of profenophos treated Anabas testudineus. The histological alterations in the several tissues of fish could be used as an important tool for assessment of pesticide pollution.