Reversible addition fragmentation chain transfer (RAFT) polymerizations of styrene in fluid CO2 have been carried out at 80 °C and 300 bar using cumyl dithiobenzoate as the controlling agent in the concentration range of 3.5·10–3 to 2.1·10–2mol·L–1. This is the first report on RAFT polymerization in fluid CO2. The polymerization rates were retarded depending on the employed RAFT agent concentration with no significant difference between the RAFT polymerization performed in fluid CO2 and in toluene. Full chain-length distributions were analyzed with respect to peak molecular weights, indicating the successful control of radical polymerization in fluid CO2. A characterization of the peak widths suggests a minor influence of fluid CO2 on the addition reaction of macroradicals on the dithiobenzoate group.