In this study, 5 and 10 mg/kg arsenic trioxide (As₂O₃) and sodium arsenate (Na₂HAsO₄) were given with subcutan route to rats. Necropsie was performed at 0.5, 1, 2, 4, 8, 12, 24, 48, 72, 96 and 120 hours after injections. Liver and kidney samples were taken and examined with histopathological methods. Sinusoidal dilatation, hemorrhage, Kupffer cell activation, degeneration and necrose of hepatocytes were observed in the liver of rats treated with both arsenic compounds. In the kidney, hemorrhage and degeneration of epithelium of proximal convoluted tubules were recorded. However, these changes were seen in arsenic trioxide treated rats earlier than those of observed in sodium arsenate treated rats. In addition, lesions in liver were earlier than in kidney.