Mass transfer processes of 2-ferrocenyl-2-propanol across a single-nitrobenzene-microdroplet/water interface were studied by laser trapping and microelectrochemical techniques. For mass transfer of the solute from water to the droplet, both fast and slow processes were observed. The mass transfer rate was governed by both adsorption of the compound on the droplet/water interface (slow) and diffusion in the water phase (fast). Kinetic parameters of the adsorption process per unit interfacial area of the droplet were determined, and the values were shown to depend on the droplet size. The observed droplet-size effect was originated from the intrinsic properties of a microdroplet. The role of adsorption of the solute on a micrometer-sized spherical liquid/liquid interface in the mass transfer processes is discussed.