Reversible addition-fragmentation chain transfer (RAFT) polymerization of methacrylic acid was successfully performed in water in the presence of a trithiocarbonate, the 4-cyano-4-thiothiopropylsulfanylpentanoic acid (CTPPA), as a RAFT agent. Several parameters such as the temperature, the concentration, the pH, the targeted polymerization degree, and the initiator concentration were studied. For pH value below the pK(a) of MAA, well-defined PMAA chains with different molar mass up to 92 000 g mol(-1) exhibiting low dispersity (D < 1.19) were obtained under a broad range of synthetic conditions.