Graphite oxide (GO) photocatalysts were derived from graphite oxidation. Absorption spectroscopy shows the increasing band gap of GO with the oxygen content. Electrochemical analysis along with the Mott-Schottky equation show that the conduction and valence band edge levels of GO from appropriate oxidation are suitable for both the reduction and oxidation of water. The photocatalytic activity of GO specimens with various oxygen contents was measured in methanol and AgNO3 solutions for H2 and O 2 evolution, respectively. The H2 evolution was strong and stable over time whereas the O2 evolution was negligibly small due to mutual photocatalytic reduction of the GO with upward shift of the valence band edge under illumination. The conduction band edge of GO showed negligibly change with the oxygen content. When NaIO3 was used as a sacrificial reagent to suppress the mutual reduction mechanism under illumination, strong O2 evolution was observed over the GO specimens. The present study demonstrates that chemical modification can easily modify the electronic properties of GO for specific photosynthetic applications.