A 4-year-old castrated male Persian cat with three years history of inflammatory and ulcerative lesions in the gingiva and periodontal areas of the right up jaw was referred to a veterinary clinic in Isfahan city of Iran. The clinical signs included gingival ulceration, oral pain, inappetence, ptyalism, halitosis, and chronic loss of weight. The condition was diagnosed clinically as Feline Chronic Gingivostomatitis. Feline Chronic Gingivostomatitis is an immune-mediated inflammatory condition and a painful, debilitating disease of cats. For confirmation of diagnosis, the lesions were sampled for histopathologic examination. Histopathologic examination revealed a chronic inflammatory reaction with infiltration of plasma cells and Lymphocytes predominantly and variable numbers of neutrophils and macrophages. The presence of immune cells in the lesions was followed up by immunohistochemistry for CD3, CD79a, and IgG. The most dominant cells in the lesions were CD79a+ and IgG+ plasma cells. The CD3+ cells incidence concerning the severity of the lesion was high as well. تفاصيل المقالة