This study was undertaken to investigate the ultrastructure of the neurons, neuroglial cells and capillaries in the area postrema[AP] of the Oriental discolured bat, Vespertilio superans. The AP of the bat was a single midline structure at the most caudal portion of the fourth ventricle. Most neurons in the AP were small cells, but their ultrastructure were similar to the typical neurons located elsewhere in the central nervous system. Astroglial cells and oligodendrocytes were also observed and showed their typical ultrastructure. Ultrastructural features of neurons, astroglial cells and oligodendrocytes were not changed during hibernating cycles. However, microglial cells were only found in the hibernating AP ; these cells were located in the parenchyma and near the blood vessels of the AP. Since the microglial cytoplasm was filled with phagocytotic inclusions, the nuclei of the these cells were eccentrically located. Phagocytotic cytoplasmic inclusions were shown to be composed of a dense irregular peripheral region and the pale round central region. A Large vacant space was often found in the electron lucent central region. Continuous and fenestrated capillaries surrounded by pericytes were found in the bat`s AP. Especially, Phagocytotic inclusions were found in the pericyte cytoplasm of the hibernating AP, and this result supports suggestion that pericytes might be phagocytotic cells. On the basis of the distributions of phagocytotic tells[pericytes and microglial cell], ultrastructure of these cells, morphology of their cytoplasmic inclusions, and the appearance of phagocytotic activity of the pericytes during the hibernating stage when microglial cells were observed, it can be concluded that pericytes may also participates in the formation of rrlicroglial cells. Tanycytes were also found in the bat AP.