Introduction: Polyoxometalates (POMs) are a group of inorganic complexes of early transition metals and oxygen atoms. These compounds have has been suggested to have some important medical applications including antiviral, antibacterial, antitumor and antidiabetic activities. Diversity of structure of the compounds that belong to the group of the materials is continuously widening with the introduction of new POMs in the scientific literature. Before one can ascribe any medical application to a newly synthesized chemical compound, toxicity studies of the material should be conducted in living systems. Therefore, the purpose of the present study was to evaluate acute toxicity of a newly synthesized polyoxomolibdate: (NH4)12[Mo36 (NO) 4 O108 (H2O) 16]. Methods: Acute toxicity study was conducted according to OECD protocol no.420 using the fixed-dose method. Before starting the test a sighting study showed that starting dose was 50 mg/kg. Male rats were grouped into four groups (n=5). One group received intraperitoneal saline and the other three groups received polyoxomolibdate doses of 5 and 50 mg/kg. Then, the signs of morbidity and mortality were monitored for 14 consecutive days. Results: None of the animals that received the doses of 5 and 50 mg/kg died before day 14 of the experiment. The animals that received the dose of 300 mg/kg showed great suffering, and the animals sacrificed immediately after the appearance of the signs. Histopathological evaluation of the liver of the animals showed some pathological changes like focal necrosis in the liver tissue and extravasation in the The 3rd International Congress on Biomedicine Hold on 6th - 14th November 2019 www.icbcongress.com central veins of liver lobules. These changes were more severe in those animals that received the higher dose of the substance. Kidney analysis showed some pathologic damages like kidney fibrosis. Conclusion: Acute toxicity study demonstrated that this newly synthesized polyoxomolibdate, (N
