Microvesicles (MVs) and exosomes, which are shed from cells as a cell-to-cell communication tool, are possible vehicles for navigating RNA molecules to body tissues. It is considered that intravenous injection of such MVs or exosomes from patients would not cause severe not-self and toxic reactions. Previously, we found that macrophages take up liposome-entrapped RNA molecules, some of which remain undegraded in the cells. Here, we demonstrate that transfected RNA molecules in human monocytic leukemia THP-1 cells were shed from THP-1 macrophages as contents in MVs during incubation in serum-free medium, which shedding was shown by biochemical analyses such as quantitative reverse transcription (qRT)-PCR, expression of TSG101 (a membrane-associated exosomal protein), and immunoelectron microscopic study. More chemically modified RNA molecules (miR-143BPs) entrapped by MVs (MV-miR-143BPs) were secreted from THP-1 macrophages after miR-143BP transfection compared with the amount after transfection with nonmodified miR-143 transfection. Furthermore, we show that the THP-1 macrophages, which were transfected with the miR-143BP ex vivo, secreted MV-miR-143BPs in xenografted nude mice after intravenous injection, because miR-143 levels were significantly increased in the serum, tumor, and kidney of the host animals. These data suggest that some of the transfected miR-143BPs were secreted from THP-1 macrophages as MV-RNAs both in vitro and in vivo.