We investigated the valence band structure of poly(sodium 4-styrenesulfonate) intercalated graphite oxide composites by photoemission spectroscopy. Typical sp(2) hybridized pi state near Fermi level as seen in graphite was compressed, indicating a charge transfer from sp(2) carbon to oxygen bonded to the carbon backbone. A downshift of highest occupied molecular orbital of the composites opened a gap of 1.24 eV below Fermi level. Work function of the composites obtained from the secondary electrons cutoff was smaller than that of graphite oxide by 0.4 eV, explaining the high performance of electric double layer capacitance of the composites compared with graphite oxide. (c) 2013 Elsevier B.V. All rights reserved.