Background and aim: Abomasal coccidiosis has been reported in sheep and goats from different countries of the world. Generally, these infections are found incidentally and characterized by the presence of giant schizonts in the abomasum mucosa. In a few studies, duodenum is also affected by Eimeria (Globidium) gilruthi. To our knowledge, there is no report on abomasal coccidiosis from Iran and this study describes gross and histopathological findings of the infection. Materials and methods: Abomasal samples of a female, 3-year-old sheep was referred to Pathology Department due to proliferative lesions. The clinical diagnosis was ostertagiosis. For microscopical examination, the samples were fixed in 10 percent buffered formalin and processed according to the standard histological techniques for paraffin embedding. Sections of 5 micrometers thickness were cut and stained with conventional hematoxylin and eosin (HE) method. Results: Macroscopically, proliferative lesions were found on the mucosa of the Abomasum. Histopathological examinations of the lesions revealed a couple of megloschizonts within the tunica mucosa of the affected abomasum. These schizonts contained a lot of merozoites and had thick cyst walls. A mononuclear inflammatory reaction was observed around the schizonts. Conclusion: According to gross and histopathological characteristics, the disease was diagnosed as abomasal coccidiosis and in case of abomasal ostertagiosis, coccidiosis should be considered as differential diagnosis.

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