We demonstrated a dispersion reversible chain transfer catalyzed polymerization (dispersion RTCP) of methyl methacrylate (MMA) with 1-phenylethyl iodide (PE-I) as chain transfer agent and GeI4 as catalyst in supercritical carbon dioxide (scCO(2)), where the PE-I was known as noneffective chain transfer agent for polymerization of MMA in RTCP. The dispersion RTCP in scCO(2) proceeded with control/livingness. On the other hand, in bulk system (bulk RTCP) and in dispersion iodine transfer polymerization (dispersion ITP) in scCO(2) under the same conditions except for GeI4, no livingness was maintained. From these results, it was assumed that the reason for the living character in the dispersion RTCP in scCO(2) is based on an accelerated reversible chain transfer reaction in scCO(2). Based on the insight, when the dispersion RTCP of MMA was carried out at higher scCO(2) pressure, poly(MMA) (PMMA) having a narrower molecular weight distribution was obtained because of the higher degree of PMMA plasticization by scCO(2). Moreover, we advanced the idea to synthesize polystyrene (PS)-b-PMMA, of which synthesis was difficult in homogeneous systems, by seeded dispersion RTCP of MMA with PS-I as macro-chain-transfer agent and GeI4 as catalyst in scCO(2).