Exosomes are membrane-bound 50-100 nm vesicles released from many cell types including normal and tumorous tissues. Exosomes transport mainly miRNAs, mRNAs, enzymes, cytokines, etc. from the cells of origin to the neighbor cells mediating the communication between them. The content of exosomes can be explored using RNA profiling after their isolation from medium conditioned by cultured cells or from other biofluids. This chapter includes detailed discussion on isolation, characterization, and miRNA profiling of exosomes. First, exosomes are isolated by filtration and ultracentrifugation, and then characterized using immunoblotting and transmission electron microscope. Finally, we used low density arrays to profile exosomal miRNA.