The new role of graphene (GR) in boosting the two-electron reduction of O-2 to H2O2 has been first identified in the GR-WO3 nanorod (NR) nanocomposite photocatalysts, which are fabricated by a facile, solid electrostatic self-assembly strategy to integrate the positively charged branched poly(ethylenimine) (BPEI)-GR (BGR) and negatively charged WO3 NRs at room temperature. Photoactivity test shows that, as compared to WO3 NRs, BGR-WO3 NRs with an appropriate addition ratio of GR exhibit remarkably enhanced and stable visible-light photoactivity toward the degradation of Rhodamine B. Besides the common roles of GR observed in the GR-based composite photocatalysts in the literature, including enhancing the visible-light absorption intensity, improving the lifetime and transfer of photogenerated charge carriers, and increasing the adsorption capacity for reactants, we have observed the new role of GR in boosting the two-electron reduction of O-2 to H2O2 in this specific BGR-WO3 NR photo catalyst system. Importantly, this new role of GR does contribute to the overall photoactivity enhancement of BGR-WO3 NR nanocomposites. The synergistic contribution of GR on improving the photoactivity of WO3 NRs and the underlying reaction mechanism have been analyzed by the structure-photoactivity correlation analysis and controlled experiments using radicals scavengers.