Atrazine (2-chloro-4-ethylamino-6-isopropylamino 1,3,5-triazine) is a widely used selective herbicide.Due to its persistence, it is present in the surface waters, contaminating non-target organisms such as fish.Herbicide atrazine was administered to Labeo rohita fingerlings in 120 hours. The used dose of atrazine was 0.18 mg/l for 120 hours (LC₀). The histopathological changes in the gill tissue like epithelial hyperplasia, curling of secondary lamellae and changes in chloride cells, besides these changes pyknotic nuclei, vacuolization,degradation of epithelial cells and pillar cells, were noticed. American-Eurasian Journal of Scientific Research 4 (3): 219-221, 2009. K. Jayachandran and K. Pugazhendy. Department of Zoology, Annamalai University, Annamalainagar-608 002. Tamil Nadu, India.