Abstract: A copper containing polyoxometalate (POM) Cu₅(OH)₄(H₂O)₂(A-a-SiW₉O₃₃)₂^10- (compound1) was synthesized and characterized. Compound 1 was tested as the first catalyst for O₂ production via electrocatalytic water oxidation. Meanwhile, compound 1 shows oxygen evolution activity and excellent stability in an acidic medium (pH=4.2). Multiple experiments including cyclic voltammetry, bulk water electrolysis, scanning electron microscope and energy-dispersive X-ray spectrometry measurements results confirm that the difference of the catalytic water oxidation activity and catalytic behavior using compound 1 and CuCl₂ is compelling evidence that compound 1 is a true active species in the electrocatalytic system.