Histology, the structural science serves to complement anatomy, physiology and pathology as well as functioning of tissues and organs of living organism. The histological structure of gill was found to be badly affected due to pesticides, after acute and chronic exposure. Histopathological changes induced by sublethal (96 hours LC₅₀/10) exposure to Bifenthrin (0.1253 ppm) and Bioneem (16.7455 ppm) on the gills of a fresh water fish Garra mullya (Sykes) were studied. Degenerated secondary gill filament, appearance of necrotic tissue, atrophy of secondary lamellae and separation of epithelial cells are the lesions seen in Bifenthrin exposed fishes. While Bioneem though biopesticide, prolonged application resulted in lamellar necrosis and hypertrophy of secondary lamellar cells at the base. Changes are more pronounced in Bifenthrin treated fishes than in Bioneem.