en Occupational Health Original Article <div style="text-align: justify;"><span style="font-family:arial;"><strong>Background:</strong> With the spread of nanotechnology, various nanoparticles with new and emerging properties have been produced and the potential toxic effects of the majority of these particles remains still unknown. The present study was conducted to determine the toxicity of Molybdenum Trioxide nanoparticles in blood and body tissues of male Wistar rats<span dir="RTL">.</span><br> <strong>Materials and Methods:</strong> Thirty Wistar rats with an average weight of 200&plusmn;10 g were included in the present experimental study; the rats were divided into three groups of control, low dose intervention and high dose intervention. Nano-trioxide molybdenum was injected at 5 and 10 mg/kg body weight for 28 days; then, blood samples and rats organs were collected to measure the molybdenum content. Molybdenum concentration was measured by atomic absorption method. The collected data were analyzed using SPSS (Version 20) and appropriate statistical methods including one-way ANOVA were used in order to compare the mean of blood variables among the groups.<br> <strong>Results:</strong> The results showed that decreasing hematocrit (p <0.001), hemoglobin (p <0.001), and red and white blood cells (p <0.01) in rates receiving 10 mg of Molybdenum trioxide nanoparticles was significantly higher than that among rates in the other two groups. The mean degradation of molybdenum trioxide nanoparticles in the liver and kidneys was significantly higher than the heart and stomach (p <0.05)<span dir="RTL">.</span><br> <strong>Conclusion:</strong> The results of the study showed that molybdenum trioxide nanoparticles at high concentrations had a more toxic effect on blood and serum parameters in comparison with the low concentrations.</span></div> Toxicity,Nanoparticles,Molybdenum Trioxide,Wistar Rats, 233 239 http://johe.rums.ac.ir/browse.php?a_code=A-10-37-8&slc_lang=en&sid=1 Majid Akhondipour m.akhondipour@yahoo.com 22400319475328460010611 22400319475328460010611 No School of Health, Kerman University of Medical Sciences, Tehran, Iran. Kerman University of Medical Sciences Ali Faghihi Zarandi 22400319475328460010612 22400319475328460010612 No Department of Occupational Health, Kerman University of Medical Sciences, Kerman, Iran. Kerman University of Medical Sciences Asghar Amirri 22400319475328460010613 22400319475328460010613 No Department of Chemistry, Payame Noor University, Tehran, Iran. Payame Noor University Nasser Gommnami gommnami_nasser@yahoo.com 22400319475328460010614 22400319475328460010614 Yes Medical School, Islamic Azad University, Mashhad Branch, Mashhad, Iran. Islamic Azad University, Mashhad Branch Reza Vazirinejad rvazirinejad@yahoo.co.uk 22400319475328460010615 22400319475328460010615 No Social Determinants of Health Research Center, Rafsanjan University of Medical Sciences, Rafsanjan, Iran. Rafsanjan University of Medical Sciences