Anodic oxygen evolution reaction (OER) is essential to participate in diverse renewable energy conversion and storage processes, while most OER electrocatalysts present satisfactory catalytic performance in only alkaline or acidic medium, limiting their practical applications in many aspects. Herein, we have designed and prepared Ir-CeO₂-C nanofibers (NFs) via an electrospinning and a relatively low-temperature calcination strategy for OER application in both alkaline and acidic conditions. Density functional theory (DFT) simulations demonstrate the high catalytic active sites of Ir atoms for OER, and that the formation of Ir–O bonds at the interface between Ir and CeO₂ can modulate the electron density of the relevant Ir atoms to promote the OER activity. In addition, the unique nanofibrous heterostructure increases the exposed active sites and promotes the electrical conductivity. Therefore, the prepared Ir-CeO₂-C nanofibrous catalyst delivers an excellent OER property in both alkaline and acidic solutions. Impressively, the overpotentials to reach 10 mA·cm⁻² are only 279 and 283 mV in the alkaline and acidic electrolyte, respectively, with favorable long-term stabilities. In addition, the two-electrode overall water splitting set-ups equipped with Ir-CeO₂-C NFs as anode and commercial Pt/C as cathode provide a cell voltage of 1.54 and 1.53 V to drive 10 mA·cm⁻² in the alkaline and acidic electrolyte, respectively, which are much lower than Pt/C||IrO₂ and lots of transition metal oxides-based electrolyzers. This research presents an efficient means to design OER catalysts with superior properties in both alkaline and acidic solutions.