Chromium-iridium oxide (CrxIr1−xO2) alloys with a wire-in-tube morphology were primally prepared as highly efficient electrocatalysts for the oxygen evolution reaction (OER) via a simple electrospinning method. The synthetic processes with an optimized annealing temperature and a rate of calcination process were finely controlled to shape a distinct double-shell nanotube architecture. A low iridium-content oxide alloy (CrxIr1−xO2 with Cr : Ir atomic ratio of 62 : 38) derived from electrospinning and the post-calcination process was the first to reveal the remarkable OER performances in alkaline solution. Moreover, it maintained the performance throughout the long-term chronopotentiometry test at a constant current density of 10 mA cm−2 without any deterioration. In particular, density functional theory (DFT) calculations prove that the Cr-rich catalyst improves the binding of OOH species on the (110) facet of the CrxIr1−xO2 surface and lowers the Gibbs free energy barrier of the OER process with superior electrocatalytic activity based on the mechanistic inspection of the electrochemical processes.