The experimental study of pseudomonas otitis media was done in animal model from the clinical and pathological points of view. The animal model was developed at a concentration of 10⁹ organisms/ml (0.05ml) in 120 rats by innoculation of pseudomonas aeruginosa (SL-45 strain) into the bulla through tympanic membrane. The clinical findings and inflammatory changes of the mucoperiosteum, bony wall of the bulla, ossicles, round window membrane, tympanic membrane, and tympanic cavity were studied as regards the correlated or interrelated changes of various stages in longitudinal studies. As the clinical findings otorrhea was seen at 3 days after innoculation and diminished at 1 week. Aural abscess was appeared at 1 to 2 weeks after innoculation and subsided at 4 weeks. Tympanic adhesion and retraction were developed from 4 weeks and persisted in 12 week animals. As the histopathological findings, three day animal showed a mild inflammatory changes with infiltration of acute inflammatory cells and hemorrhage in the mucoperiosteal lining. One week animal showed granulomatous changes on the mucoperiosteal lining with heavy infiltration of acute inflammatory cells, and periosteal reaction was marked. In two week animal mucus secreting cells and subepithelial gland-like structures showing positive PAS reaction were developed, and new bone formation was appeared. Three and four week animals showed marked increase of goblet cells and ciliated columnar epithelium, and increased subepithelial fibrosis. Bone destruction and reconstruction were prominent. In six and eight week animals inflammatory reaction in subepithelial space was diminished and epithelial lining was changed into cuboidal or flat cells. And organized exudates were seen in the bulla. In twelve week animal inflammatory reaction was diminished and dense fibrous subepithelial changes were prominent with decreased neo-osteogenesis. Cholesterol crystals at round window niche and tympanic cavity were found, and epitympanic retraction pocket was noted in this animal group. In a concentration of 10¹¹/ml animal death, tympanogenic labyrinthitis, and cochlear destruction were found. The similarity of findings between human and animal otitis media were observed in this study. This animal model will be used in the further study of pathogenesis of otitis media as an ongoing project.