Squamous cell carcinoma is a malignant tumor of epidermal cells in which the cells show differentiation to keratinocytes. The tumor is common in the horse, cow, cat, and dog, but relatively uncommon in the sheep, and rare in the goat and pig. Oral squamous cell carcinomas occur particularly in old cats and dogs. They may involve the epithelium of the tonsillar crypts, the gingiva, or the lateral margins and ventral surface of the tongue. A 3–year-old ewe due to presence of an oral haemorrhagic mass with the history of reduced appetite, weight loss and halitosis was referred to the Veterinary clinic of Islamic Azad University of Shahrekord. Grossly, the tumor mass was located in the floor of mouth posterior to the incisors and caused displacement of the left second intermediate and corner incisors. The ulcerated mass, measuring approximately 4.5Ð2.5 cm, was irregular, cauliflower like, red-black, friable, and did not show metastatic spread to the regional lymph nodes. Mild bone destruction was seen in the radiogram of mandible adjacent to the tumor. For histopatological examination, biopsy was performed, processed routinely and stained with haematoxylin and eosin. Histopathological examination of the excisional biopsy revealed irregular cords and clusters of pleomorphic neoplastic cells. These cells had vesicular nuclei, prominent nucleoli, and abundant cytoplasm. There was no evidence of keratin pearl formation and only a few individual cells keratinization were observed. Nuclear hyperchromatism, karyomegaly, and numerous mitotic figures were seen in the some sections. Based on gross and histopathological characteristics, the tumor was diagnosed as poorly differentiated oral squamous cell carcinoma. To the best of our knowledge, only one squamous cell carcinoma of the gum has been reported in the sheep and this case is unusual due to the site of development.

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