For the purpose of evaluating the harmful effect of di-methyl mercury, the well-known pollutant of the aquatic ecosystem, on liver and kidney of mammals with its both short- and long-term toxicity models, the goal was achieved by using twenty-four mature albino male rats, aged between 10 and 12 weeks, which were divided into 3 groups (8 rats for each). These included a control group, group 1 for chronic toxic effects (treated with a 2.5 mg/kg daily dose of di-methyl mercury for 30 days), and group 2 for acute toxic effects (treated with a 5 mg/kg daily dose of di-methyl mercury for 15 days). Four animals of each group were euthanized, and the others were kept to be sacrificed after 30 days as a recovery period. The sections were prepared from liver and kidneys, stained and examined to record and to grade the intensity of histopathological changes. Liver sections elucidated mild to moderate pathological changes in both treated groups, including vacuolar degeneration of hepatocytes, foci of coagulative necrosis, and inflammatory cell deposition mainly composed of lymphocytes, plasma cells and macrophages in peri-portal and Peri-central and peri-sinusoidal areas. Also, the vascular reaction, as hyperemic portal arteries, congested sinusoids and central veins, was present with Kupffer cell proliferation. Cholangitis or cholangiohepatitis were observed in 2.5 and 5 mg methyl mercury-treated groups as a solitary case at the end of exposure or after the recovery period. The examination of the kidney sections explored adverse changes manifested by vascular congestion, cloudy swelling of the renal tubular epithelium, protein cast in the renal tubules, interstitial nephritis and multifocal hemorrhage at the cortex and medulla; these changes were apparent at both acute and chronic models of toxicity. It was clear that the recovery period was not enough to exclude or reverse the toxic effects of methyl mercury because the same changes were present at the end of the recovery period.