The complexes formed between the cationic graft copolymer of poly(ethylene oxide) and poly(ethyleneimine) (PEO-g-PEI) and alkyl sulfate surfactants were studied using potentiometric titration, fluorescence spectroscopy, zeta-potential measurement, dynamic light scattering, and electron microscopy. In contrast to the complexes of PEI homopolymer, which phase separate, the PEO-g-PEI complexes are water-soluble over the whole range of compositions of the mixture, including the electroneutral stoichiometric complexes. These species apparently represent micelle-like aggregates with a hydrophobic core from the surfactant-neutralized polyions and a hydrophilic corona from the ethylene oxide chains. This is a very different morphology compared to the previously de scribed complexes of poly(ethylene oxide)-b-polymethacrylate anions with cationic surfactants, which formed vesicles. The difference in the morphology is attributed to the difference in the copolymer architecture (branched vs linear, graft vs block copolymer, lengths of chain segments). The unique self-assembly behavior, the simplicity of the preparation, and the wide variety of available surfactant components make these systems promising in addressing various theoretical and practical problems, particularly, in pharmaceutics.