Reversible addition fragmentation chain transfer (RAFT) ab initio emulsion polymerization of styrene mediated by 2-(((dodecylsulfanyl) carbonothioyl) sulfanyl) propanoic acid was investigated with sodium dodecyl sulfate (SDS), poly(acrylic acid)(29)-b-polystyrene(5) trithiocarbonate macro-RAFT agent (PAA(29)-PSt(5)-RAFT), and poly(acrylic acid)(29)-b-polystyrene5 diblock co-oligomer (PAA(29)-PSt(5)) as the surfactant, respectively. Polystyrene latex having controlled molecular weight, relatively low PD and narrow particle size distribution was obtained by postneutralizing PAA(29)-PSt(5)-RAFT and PAA(29)-PSt(5). This result was in agreement with the superswelling hypothesis that superswollen oligomer-containing particles caused the colloidal instability in the early stage of RAFT emulsion polymerization with SDS as surfactant. The successes of PAA(29)-PSt(5)-RAFT and PAA(29)-PSt(5) were due to the high interfacial tensions of the styrene/water/surfactant systems that suppressed the superswelling and thus improved the colloidal instability. A majority of the initial RAFT molecules appeared to be converted at a low monomer conversion due to the inhibition period.