Tilapia fish, Oreochromius niloticus were exposed to different sublethal concentrations (30 mgll and 50 mg/l) of chlorine to observe behavioral alterations and histopathological alterations in liver. The fishes showed marked changes in their behavior when exposed to the test solution of different concentrations. The fishes showed rapid swimming than in control, hyperactivity, loss of balance, increased surfacing activity. The lives showed marked alterations, the focal areas of necrosis vacuolation and dilation and thrombosis formation in central vein, rupture in the hepatocytes, Cell damage, Moreover, pyknosis (PY) and hemorrhages was seen.