The acinic cell tumor developed in the right lower lip region of a 62 year-old woman was studied by scanning and transmission electron microscopes. (1) The tumor was about 0.7×0.7×0.6 cm in size, and almost spherically shaped, and its surface was covered with a thin membrane. (2) Histological observations showed that the tumor consisted of relatively large cells which contained acidophilic granules and vacuoles. The nucleus of the tumor cell was rich with chromatin. (3) Scanning electron microscopically, the tumor cell was either spherical or oval, its nucleus was situated off-centrally, and numbers of granules with varying sizes formed a beads-like, beehive-like and reticular structures in the cytoplasm. (4) Transmission electron microscopically, the cell organelle was found to be poor, and vacuole-like structures with various sizes and myelin structures were observed. (5) The patient is in good prognostic condition at the stage of 2 years after surgery, and no abnomalities such as metastasis are presently observed.