Iodine transfer dispersion polymerization (dispersion ITP) with CHI3 and reversible chain transfer-catalyzed dispersion polymerization (dispersion RTCP) with N-iodosuccinimide of methyl methacrylate were performed successfully in supercritical carbon dioxide medium. Both polymerizations proceeded smoothly to ∼80% conversion in 6 h and yielded the polymeric product as a powder after venting the reactor. In both syntheses, the number-average molecular weights (Mn) increased with greater conversion. The ratio (Mw/Mn) was maintained at comparatively low values throughout the polymerizations; the values of Mw/Mn were lower in the dispersion RTCP (1.3–1.4) than the dispersion ITP (1.5–1.7). A chain extension test using styrene indicated that the poly(methyl methacrylate) prepared by dispersion ITP and dispersion RTCP had high degrees of livingness (71 and 74%, respectively).