This paper reports the facile synthesis of highly single-crystalline IrO 2 nanowires grown on an Au microwire (IrO 2 NW-Au) and its reduced form (Ir/IrO 2 NW-Au); and their electrocatalytic activity for oxygen reduction reaction, H 2 O 2 reduction/oxidation, and dopamine (DA) oxidation. IrO 2 NW-Au, prepared by direct vapor transport process under atmospheric pressure, was reduced by H 2 gas flowing at 200°C. This additional modification resulted in the significant morphological changes from the smooth nanowire structures of IrO 2 NW-Au to substantially porous structures of Ir/IrO 2 NW-Au with sustaining the external nanowire frameworks. The compositions were also changed from mostly IrO 2 in IrO 2 NW-Au to the mixture of IrO 2 and Ir(0) metal in Ir/IrO 2 NW-Au. Ir/IrO 2 NW-Au showed highly enhanced and facilitated electrochemical reaction kinetics compared to IrO 2 NW-Au for ORR and H 2 O 2 reduction/oxidation. The ORR limiting-like current at Ir/IrO 2 NW-Au was measured to be ∼19-fold greater than that of IrO 2 NW-Au. In addition, the amperometric responses to varying H 2 O 2 concentration confirmed that Ir/IrO 2 NW-Au exhibited ∼8-fold (for H 2 O 2 oxidation) and ∼750-fold (for H 2 O 2 reduction) higher sensitivity than IrO 2 NW-Au. The observed enhanced activity of Ir/IrO 2 NW-Au could be attributed to the enlarged active surface area as well as the inherent electroactivity of Ir/IrO 2 NW material induced by co-existence of Ir oxide and metal. In contrast, more stable and decent anodic current responding to DA oxidation was measured at IrO 2 NW-Au than Ir/IrO 2 NW-Au, indicating IrO 2 rather than Ir(0) has higher catalytic activity for DA oxidation.