Exosomes are nanosized lipid membrane vesicles secreted from most, if not all types of cells. Since exosomes transfer their cargoes including proteins and nucleic acids to the cells that take up exosomes, exosomes play key roles in various biological events such as immune response and tumor metastasis. Therefore, it is expected that exosomes can be used as drug delivery system (DDS) for proteins, nucleic acids, and other bioactive compounds. In this review, we first overview the role of exosomes in biological events. Then, we introduce our study on the in vivo fate of exogenously administered exosomes. Finally, we describe the effect of exosome isolation methods on the characteristics of exosomes.