In this paper, we report on a novel family of monodisperse thermo-sensitive core–shell hydrogel microspheres that is featured with high monodispersity and positively thermo-responsive volume phase transition characteristics with tunable swelling kinetics, i.e., the particle swelling is induced by an increase rather than a decrease in temperature. The microspheres were fabricated in a three-step process. In the first step, monodisperse poly(acrylamide-co-styrene) seeds were prepared by emulsifier-free emulsion polymerization. In the second step, poly(acrylamide) or poly[acrylamide-co-(butyl methacrylate)] shells were fabricated on the microsphere seeds by free radical polymerization. In the third step, the core–shell microspheres with poly- (acrylamide)/poly(acrylic acid) based interpenetrating polymer network (IPN) shells were finished by a method of sequential IPN synthesis. The proposed monodisperse core–shell microspheres provide a new mode of the phase transition behavior for thermo-sensitive “smart” or “intelligent” monodisperse micro-actuators that is highly attractive for targeting drug delivery systems, chemical separations, sensors, and so on.