The choroid plexus (ChP), located within each brain ventricle, are the primary source of cerebrospinal fluid (CSF), and play an important role in maintaining central nervous system (CNS) homeostasis. ChP acts as a functional immunological interface between the blood and the CSF, and functions as a gateway for the transmigration of bone marrow-derived leukocyte into brain parenchyma. Thus, ChP harbors a several immune cells like macrophages, dendritic cells, monocytes, neutrophils, and lymphocytes. Macrophages represent the largest population of immune cells in the ChP and transcriptome studies have shown that three different kind of macrophages reside in ChP of which epiplexus macrophage (ChP-epiplexus-macrophage) resemble microglia. However, the origin of ChP-epiplexus macrophage remains unknown. As fate mapping using genetic tool cannot distinguish epiplexus macrophage from microglia, we devised microglia transplantation experiment into brain parenchyma to determine the ChP-epiplexus-macrophage origin. We reveal that microglia migrate to and become ChP-epiplexus-macrophage. Our findings raise an interesting possibility that microglia may migrate from brain parenchyma to ChP to become ChP-exiplexus macrophage, where they communicate with peripheral immune cells, playing important role in regulation of physiological and pathophysological functions both in the brain and peripheral organs.