A RAFT agent bearing a carboxylic acid group is applied to the miniemulsion polymerization of methyl methacrylate (MMA) in order to prepare the stability-enhanced functionalized latex. At the polymerization temperatures of 60, 70, and 80 degreesC, the polymerization kinetics, evaluation of the molecular weight, and PDI are found to be strongly dependent on the temperature. The higher the temperature, the faster the polymerization rate, the lower the molecular weight, and the lower the PDI are obtained. The PMMA nanoparticles prepared by the miniemulsion polymerization using this RAFT agent show some interesting characteristics. As the amounts of the RAFT agent increase, the magnitude of the zeta potential and the conductivity correspondingly increase and the size of the PMMA nanoparticle decreases from 118.8 to 49.5 nm. These results imply that the carboxyl group (or partially in anionic form) is present on the surface of the polymer particles, and therefore, the stability of the system is enhanced. Furthermore, no noticeable sign of creaming or destabilization of the PMMA nanoparticles was observed for at least several months by remaining as a homogeneous latex.