SummaryAbout 160 cases of odontogenic tumor were studied histologically and a classification of the odontogenic tumor was presented. No clear‐cut example of melano‐ameloblastoma, odontogenic sarcoma, ameloblastic neurinoma, dentinoblastoma was observed in this study.About a half of the ameloblastoma belonged to Type III. Ameloblastoma of the maxilla was principally Type I. More differentiated types were found mostly in the younger patients. For the reason of a predirection of the ameloblastoma in the mandibular molar region, the developmental relationship between tooth band and jaw bone in this region should be considered. Cyst in the parenchyma might be produced in three ways; keratinous degeneration of the squamous epithelial portion, fine granular lipo‐protein or glucolipid degeneration of the epithelium without keratinous changes, and hydropic degeneration of the stellate reticulum. Hyalinous halo surrounding nests of epithelium indicate a simple hyalinous change of the stromal tissue adjacent to the basement membrane or true thickening of the basement membrane like membrana preformativa. Cyst formation of the stroma may be influenced not merely by circulatory disturbances of the stroma, but by some action on the adjoining epithelium.So‐called adeno‐ameloblastoma should be considered as a variant of ameloblastoma. Its adenomatous structure may be formed from atypical growth of the epithelium of dental origin and not a true glandular structure.Two cases of malignant ameloblastoma were observed in this series. In one instance metastases to the cervical lymphnodes and the upper lip were histologically demonstrated.When we diagnose the odontogenic mesodermal tumors, by means of only histological examination, we should have careful consideration in various instance.Three types of the odontogenic mixed tumor represented various differentiating grade of thetum or tissues. Ameloblastic hemangioma was supposed to be a variant of ameloblastoma with a dilatation of the stromal blood vessels and not with a true hemangio