Histological study was undertaken on ciliated craniopharyngioma and Rathke cleft cyst, to know the origin of ciliated craniopharyngioma. Subjects were 7 cases with symptomatic Rathke cleft cysts and a ciliated craniopharyngioma. Light and electron microscopic observations were made on surgically resected specimens of the 8 cases. The ciliated craniopharyngioma was composed mainly of papillary type of craniopharyngioma and of dispersed ciliated columnar epithelium including goblet cells. Four cases with Rathke cleft cyst showed squamous metaplasia of which the basal cells were histologically similar to that of papillary type of craniopharyngioma. Other 3 cases of Rathke cleft cyst, basal cells were revealed to have tonofilaments and desmosomes. It seems possible that ciliated craniopharyngioma has derived from the basal cells of Rathke cleft epithelium.