Block copolymers were prepared with two anionic polyelectrolyte blocks: sodium polyacrylate (PA) and sodium polystyrene sulfonate (PSS), in order to investigate their phase behavior in aqueous solution in the presence of Ca2+ cations. Depending on the concentration of polymer and Ca2+ and on the ratio of the block lengths in the copolymer, spherical micelles were observed. Micelle formation arises from the specific interaction of Ca2+ with the PA block only. An extensive small-angle scattering study was performed in order to unravel the structure and dimensions of the block copolymer micelles. Deuteration of the PA block enabled us to perform contrast variation experiments using small-angle neutron scattering at variable ratios of light and heavy water which were combined with information from small-angle X-ray scattering and dynamic light scattering.Graphical Block copolymers with two anionic polyelectrolyte blocks, sodium polyacrylate (PA) and sodium polystyrene sulfonate (PSS) self-assemble in response to an addition of Ca2+ cations. Deuteration of the PA block made possible contrast variation experiments using SANS at variable ratios of H2O/D2O, which in combination with SAXS revealed the morphology of the self-assemblies.