Dispersion polymerization was applied to the controlled/living free-radical polymerization of styrene with a reversible addition-fragmentation chain transfer (RAFT) polymerization agent in the presence of poly(N-vinylpyrrolidone) and 2,2-azobisisobutyronitrile in an ethanol medium. The effects of the polymerization temperature and the postaddition of RAFT on the polymerization kinetics, molecular weight, polydispersity index (PDI), particle size, and particle size distribution were investigated. The polymerization was strongly dependent on both the temperature and postaddition of RAFT, and typical living behavior was observed when a low PDI was obtained with a linearly increased molecular weight. The rate of polymerization, molecular weight, and PDI, as well as the final particle size, decreased with an increased amount of the RAFT agent in comparison with those of traditional dispersion polymerization. Thus, the results suggest that the RAFT agent plays an important role in the dispersion polymerization of styrene, not only reducing the PDI from 3.34 to 1.28 but also producing monodisperse polystyrene microspheres. This appears to be the first instance in which a living character has been demonstrated in a RAFT-mediated dispersion polymerization of styrene while the colloidal stability is maintained in comparison with conventional dispersion polymerization. (c) 2006 Wiley Periodicals, Inc.