Block copolymers composed of methacrylic acid (MAA) and methyl methacrylate (MMA) blocks are interesting candidates for replacing surfactants in emulsion polymerization methods. Here the synthesis and experimental characterization of well-defined PMAA-PMMA block copolymers made via RAFT polymerization are reported. It is shown that these block copolymers self-organize in water into micellar spherical or cylindrical structures or into highly size disperse structures (probably vesicles) in aqueous salt solutions upon increasing the pH. The physical properties of the polymer dispersions depend on the self-organization morphology which is determined by the diblock copolymer PMAA and PMMA block lengths. The relation between diblock copolymer block lengths and the self-organized structures is rationalized using self-consistent field theory (SCFT). Theoretically predicted self-assembled structures of MAAx-MMAy block copolymers are compared with the results obtained from experiments. Size and morphology of the self-assembled structures are in good agreement with SCFT.