Study was conducted to assess the histopathological damage of Gill, Liver and Brain in common carp, Cyprinus carpio after sublethal exposure to Quinalphos. Exposed to sublethal concentration (One tenth (1/10th, 0.75 µl/L) of commercial grade quinalphos (25% Emulsified Concentration) for 1, 7, 14, 21 and 30 days and a parallel control was run simultaneously. Gill, Liver and Brain of exposed individuals exhibited some remarkable changes in their histology in comparison to control. Prominent changes include shrinkage of the glomerulus, and dilation of tubular lumen. Vacuolization, desquamation, hydropic swelling and hyaline degeneration of tubular epithelium is also observed. Cyst formation and hemorrhage also appear in certain specimens. Duration of exposure appears to have a profound effect on Gill, Liver and Brain as with increasing duration of exposure histopathological damages become more severe.