The present study was made to investigate the effect of chromium on the histopathological study in the gill tissue of fresh water fish, Oreochromis mossambicus. The fish exposed to chromium (2 ppm) for 10 days, 20 days and 40 days. The present study shows the breakage of lamellae and separation of lamellae was noted in the gill tissue for 20 days and 40 days respectively. The present study concludes that the increasing concentration chromium damages the gill tissue of Oreochromis mossambicus.