Eosinophilic otitis media is an intractable otitis media and a fairly common middle ear disease. However, the pathogenesis of eosinophilic otitis media is obscure.To observe the pathological and ultrastructural changes of the Eustachian tube mucosal epithelium in rats with eosinophilic otitis media and further explore the pathogenesis of eosinophilic otitis media.Animals were intraperitoneally injected with 2000 mg ovalbumin and 100 mg aluminum hydroxide (alum) on day 0, followed by 100 mg ovalbumin and 100 mg alum injection on days 7 and 14. Next they were topically boosted by daily application of 100 mg ovalbumin solution via nasal drip and intratympanic injection of 0.1 mL ovalbumin (1000 mg/mL) in the right ear (group A, n = 80) and 0.1 mL saline in the left ear as control (group B, n = 80) starting on day 21 and continuing for 14 days. The temporal bones were dissected on the 35th, 38th, 41st and 43rd day separately under anesthesia. Scanning electron microscopy, hematoxylin-eosin and toluidine blue staining were used to observe the pathological and morphological changes of Eustachian tube mucosa stained samples. Moreover, inflammatory cells and cilia were counted.The epithelium of the Eustachian tube in group A was swollen and thickened. The cilia were arranged in a disorderly manner and partially detached. Eosinophils infiltrated the submucosal layer of the Eustachian tube, and their number increased significantly compared with that in group B (p < 0.05). Simultaneously, mast cell degranulation was observed in group A. Scanning electron microscopy revealed that the cilia were lodged and gathered along the whole length of Eustachian tube in group A. Ciliated cell density was significantly lower than that in Group B (p < 0.01).In the eosinophilic otitis media model, allergy caused significant changes in pathology and morphology of the Eustachian tube mucosa, affecting the normal function of the Eustachian tube which played an important role in the occurrence and development of eosinophilic otitis media.Copyright © 2020 Associação Brasileira de Otorrinolaringologia e Cirurgia Cérvico-Facial. Published by Elsevier Editora Ltda. All rights reserved.