Dynamic light scattering, scanning electron microscopy, and turbidity measurements have been applied in the investigation of nanoaggregate formation of poly(ethylene oxide)-b-polymethacrylate (PEO-b-PMA) in which the PMA block is electrically neutralized with alkaline earth metal ions. They self-assemble to form micelle-like nanoaggregates comprised of a "core" of neutralized polyions surrounded by the PEO "corona". The nanoaggregates have properties of both amphiphilic block copolymer micelles and polyelectrolyte complexes. The significance of these new types of nanoaggregates is that they can incorporate ionic compounds into their cores, in quite contrast to conventional polymer micelles in which only hydrophobic species can be incorporated into the core in aqueous solutions. The potential applications of these systems include a carrier for ionic drugs and a nanoreactor for chemical reactions of ionic species.