The transfer of an electrochemically-produced ferrocenium cation across a hydrophobic ionic liquid (IL) microdroplet/water interface was kinetically studied by a recessed microelectrode. Cyclic voltammograms of ferrocene in an IL microdroplet injected into a cylindrical recess on a microelectode in water were measured as a function of the phase-boundary potential between the IL and water phases. The transfer rate constant of the ferrocenium cation at the IL/water interface could be determined by the digital simulations as well as a simple estimation based on the efficient diffusion in the micrometer-sized droplet system. The ion transfer rates were analyzed by the Butler-Volmer equation and were significantly influenced by the type of the IL. The IL dependence on the ion transfer rate is discussed in terms of the physical properties of the ILs. (C) 2011 Elsevier B.V. All rights reserved.