The behavior of mixed poly(methacrylic acid)/poly(ethylene oxide) (PMA/PEO) shells of hybrid polymeric micelles with polystyrene cores was studied in detail by a combination of light scattering, fluorometric, potentiometric, and other techniques. The results show that the dissociation of poly(methacrylic acid) in the inner layer close to the polystyrene core is suppressed, in part because of the relatively low polarity of the medium and because of a high concentration of carboxylic groups. The dissociation degree does not correspond to the bulk pH. The PMA chains form a hydrogen-bond-stabilized interpolymer complex with PEO chains in the inner shell. The compact layer of the PMA-PEO complex around the polystyrene core is very stable and resistant to changes in the bulk solvent properties. Potentiometric titration shows that an important fraction of PMA, which is engaged in the complex formation, cannot be neutralized even in a considerable excess of the base. The peripheral part of the layer is formed preferentially by the stretched and ionized free ends of the PMA blocks. Hybrid PS-(PMA/PEO) micelles resemble so-called "onion type" micelles, for example, polystyrene-block poly(2-vinylpyridine-block-poly(ethylene oxide)) [see: Prochazka et al. Macromolecules 1996, 29, 6526.] and may be regarded as "pseudo-multilayer" polymeric nanoparticles.