The electrochemistry of ferrocene (FeCp) in a single micrometer-sized nitrobenzene droplet dispersed in water was studied by laser trapping and microelectrochemical techniques. Mass transfer of FeCp, ferrocenium ion, and tetra-n-butylammonium ion between the droplet and water phases accompanied by oxidation of FeCp proceeded across the dropletwater interface. The peak potential of a cyclic voltammogram of FeCp was highly dependent on the potential sweep rate. The potential shift was analyzed by thin-layer electrolysis and the results are discussed in terms of the irreversible electron transfer of FeCp across the dropletelectrode interface and in terms of mass transfer of ion species across the dropletwater interface.