Artificial photosynthesis has attracted attention as one of solutions to energy and environmental problems. A catalyst for water splitting into hydrogen and oxygen in artificial photosynthesis is important to be developed. In this context, much effort has been paid for development of molecular catalysts for water oxidation. There are only a few reports on a catalyst for hydrogen peroxide production via water oxidization. Herein we report catalytic hydrogen peroxide production via water oxidization by a dinuclear ruthenium complex. We found that for this dinuclear ruthenium (II) complex, an OOH bridging is formed oxidatively from OH and H2O ligands in basic conditions. The activity and mechanism of catalytic hydro peroxide evolution in homogeneous solution will be discussed.