Effect of cadmium (Cd), chromium (Cr) and mercury (Hg) on the gill histology of Clarias batrachus L. was investigated following 28 days exposure to their sublethal concentrations under laboratory condition. Hyperplasia and hypertrophy of the lamellar epithelium, necrosis, partial lifting of epithelial layer, damage of gill ray, oedema of primary lamellae, damage of pillar cells and congestion of blood vessels were the main histopathological changes. In Cd treated fishes the interlamellar spaces were abolished but distended gill rays were characteristics of Cr treatment. Extensive cellular and tissue damages were prominent in Hg treated fishes.