PURPOSE: To produce easily and efficiently hydrogen peroxide by allowing a metallic complex having an oxygen reducing action to react with oxygen in an organic solvent, and simultaneously or subsequently bringing the obtained soln. into contact with an aq. soln. phase contg. hydrogen ions.

CONSTITUTION: Oxygen is blown into an organic solvent such as benzene contg. a metallic complex having an oxygen action, and said metallic complex is allowed to react with oxygen to obtain a peroxy complex. Said soln. is simultaneously or subsequently brought into contact with an aq. soln. of hydrochloric acid contg. hydrogen ions and agitated, and the aq. soln. phase is separated to form hydrogen peroxide. The resulting deactivated metallic complex is electrolytically reduced in the presence of a supporting electrolyte such as sodium perchlorate, regenerated, and can be reused by circulation. A complex of a zero- valence complex of a platinum group metal shown by the formula M (AR1R2R3) (where, M is Pt, Pd, Ni, etc., A is a 5b-group element such as P, and R1, R2, and R3 are substituted or unsubstituted alkyl or aryl groups) is preferably used as said metallic complex.