Exosomes are extracellular vesicles that are released from cells and comprise microRNAs (miRNAs); however, little is known about the homogeneity of their contents. In this study, we assessed the homogeneity of exosomes by measuring the number of particles and miRNA copies released by pancreatic cancer PK-45H cells. miR-204-3p and miR-638 were abundant in the exosomes released by PK-45H cells and were present as one-to-several copies per 10,000 particles. The number of miR-638 copies released by PK-45H cells significantly declined following treatment with 10 μM GW4869, a neutral sphingomyelinase 2 (nSMase2) inhibitor. These findings suggest that exosomes form heterogeneous particle populations and nSMase2 may be involved in the exosomal uptake of miR-638.