Recently, the transfer method has been shown to be useful for preparing cell-sized phospholipid bilayer vesicles, within which desired substances at desired concentrations can be encapsulated, with a desired asymmetric lipid composition. Here, we investigated the transfer process of water-in-oil (W/O) droplets coated by phospholipid monolayers across an oil/water interface by both experimental observation and theoretical modeling. Real-time experimental observation of the transfer revealed that the transfer process is characterized by three kinetic regimes: a precontact process (approaching regime), an early fast process (entering regime), and a late slow process (relaxation regime). In addition, bigger droplets require much more time to transfer than smaller droplets. We propose a theoretical model to interpret this kinetic process. Our theoretical model reproduces the essential aspects of the transfer kinetics, including its size-dependence.