Bi2Ga4O9 shows an intrinsic dual edge of light absorption at ∼433 and ∼382 nm. The estimated valence and conduction band potentials allow water splitting. Bi2Ga4O9–0.5 wt.% RuOx photocatalyzes overall water splitting under visible light. The optimal gas generation rates are 41.5 (H2) and 19.6 (O2) μmol/h/g. The apparent quantum yield at 420 nm is 0.09%.