The object of the present invention is to provide a method for producing a resin microparticle aqueous dispersion, which can produce monodisperse resin microparticles, does not cause clogging by a product, does not require a high pressure, and has a high productivity. Thus, provided is a method for producing a resin microparticle aqueous dispersion, wherein a fluid having at least one kind of resin dissolved in a solvent with which a resin is soluble and compatible and a fluid of an aqueous solvent join together in a thin film fluid formed between processing surfaces arranged opposite so as to be able to approach to and separate from each other, at least one of which rotates relative to the other, whereby resin microparticles are obtained in the thin film fluid by way of separation/emulsification.