Chronic otitis media represents one of the most prevalent forms of infectious desease. It is a worldwide health problem which is still prevalent in the modern antibiotic era. Especially cholesteatomatous otitis media destroys the surrounding bony structure and may cause dangerous complication such as labyrinthitis, meningitis, brain abscess and facial palsy. The clinical significance of the cholesteatoma lies in its association with progressive bone destruction which requires major middle ear surgery for eradication of the infection. Otologists have been engaged in a search for answers concerning the pathogenesis and pathophysiology of cholesteatoma since the initial descriptions of Cruveilheir and Muller, and much information has been gathered over the past 140 years. The aim of this study was to clarify the structure of the various elements that compose the cholesteatoma removed at operation and to elucidate the possible mechanism of this disease by a morphologic analysis. The authors analysed 20 operated cases of cholesteatomatous otitis media with the histopathological and the ultrastructural features. The results obtained were as follows ; 1) As well as ear canal epidermis, cholesteatoma matrix consisted of squamous epithelium showing four layers of epidermis. 2) Subepithelial tissue infiltrated with inflammatory cells was noted between cholesteatoma matrix and bone, and lymphocyte was dominant in it. 3) Inflammatory cells were noted in cholesteatoma matrix, which were increased when subepithelial inflammation was intense. 4) Epithelia hyperplasia and disarray of epidermal keratinocyte in cholesteatoma matrix seemed to depend on degree of subepithelial inflammation. 5) In cholesteatoma, there were active cell divisions in stratum basale, aggregation of tonofilaments and increased keratohyaline granules, which were all suggestive of increased keratinization.