en Histology Histology Original Original <p style="text-align: justify;"><strong>Introduction</strong>: Rosmarinus officinalis is a useful medicinal plant with numerous ethnopharmacological applications and widespread use in the industry. The main constituent of this plant is essential oil. There is a misconception that there is no restriction to using medicinal plants. The present study examined the effects of the chronic administration of Rosemarinus officinalis essential oil on the liver and kidney.<br> <strong>Methods</strong>: Twenty-Eight Wistar rats were divided into 4 groups. Moreover, the study animals were Intraperitoneally (IP) injected for 21 days with 0.2%, 1%, and 2% Rosemarinus officinalis essential oil and the solvent, respectively. After this period, the study animals&rsquo; blood samples were collected for renal and hepatical biochemical evaluations. Tissue samples from these organs were obtained for histomorphometric and histopathological studies.<br> <strong>Results</strong>: The chronic treatment of animals with Rosemarinus officinalis essential oil increased blood urea nitrogen and aspartate aminotransferase in the study samples&rsquo; blood (P<0.05). The diameter of the hepatocytes distal to the central vein significantly increased, compared to the proximal ones (P<0.05). Atrophic and degenerative changes in the liver and kidney tissues were observed by 1% and 2% administration of Rosemarinus officinalis essential oil.<br> <strong>Conclusion</strong>: Our findings indicated that chronic and high administration of Rosemarinus officinalis may harm the liver and kidney.</p> Rosemarinus officinalis, Liver, Kidney, Toxicity 23 30 http://anatomyjournal.ir/browse.php?a_code=A-10-139-2&slc_lang=en&sid=1 Sahel Motaghi sahelmotaghi@uk.ac.ir 10031947532846003984 10031947532846003984 Yes Department of Basic Sciences, Faculty of Veterinary Medicine, Shahid Bahonar University of Kerman (SBUK), Kerman, Iran. Bahram Shohreh bahram_shohreh@yahoo.com 10031947532846003985 10031947532846003985 No Department of Animal Science, College of Animal Science and Fisheries, Sari Agricultural Sciences and Natural Resources University, Sari, Iran. Mohammadnaser Nazem nasernazem@yahoo.com 10031947532846003986 10031947532846003986 No Department of Basic Sciences, Faculty of Veterinary Medicine, Shahid Bahonar University of Kerman (SBUK), Kerman, Iran. Narges Ahmadusefi nargesahmadusefi@gmail.com 10031947532846003987 10031947532846003987 No Department of Animal Science, College of Animal Science and Fisheries, Sari Agricultural Sciences and Natural Resources University, Sari, Iran.