Primary carcinoma of the fallopian tube is one of the least common neoplasms arising from the female genital tract with rare preoperative correct diagnosis. Recently, we had chances to experience two cases of this tumor, one of which was examined electron microscopically. Both of them revealed the well-differentiated pattern of papillary adenocarcinoma. Electron microscopically, most of the cancer cells had pleomorphic nuclei, giant or multiple nucleoli, numerous mitochondria, poorly developed rER and abundant polysomes. Small number of cells rich in lysosome-like granules were also observed near the basement membrane. Among the cancer cells, "ultrastructural alveolar spaces", composed of several cancer cells, were prominent. In the cancer cells, there were observed the following interesting observations; annulate lamellae-like structure, unusual bundles of the filamentous elements and lamellar body-like structures. Normal tubal epithelium consisted of ciliated cells, secretory cells, peg cells and so-called "indifferent cells". The fact that the present tumor had no ciliated cells and few secretory cells indicated that this tumor was originated from "indifferent cells" or peg cells.