Uniform hierarchical Bi₂O₃/MnO₂ nanoflowers (BM NFs) are fabricated via a reaction strategy by combining redox reaction and hydrothermal treatment. This wet chemical method reports for the first time a one pot synthesis of Bi₂O₃/MnO₂ nanoflowers via a thermodynamically allowed galvanic reaction between Bi(0) and KMnO₄ in aqueous solution under modified hydrothermal (MHT) conditions. The Bi₂O₃/MnO₂ NF composites are then applied as a catalyst for electrochemical hydrogen peroxide detection. Exceedingly high H₂O₂ detection sensitivity (0.914 μA μM⁻¹ cm⁻²) lies in a wide linear range of 0.2–290 μM and the detection limit goes down to 0.05 μM (S/N = 3) for non-enzymatic detection of H₂O₂ in solution. This prototype sensor demonstrates an admirable analytical performance considering its long-term stability, good reproducibility and acceptable selectivity against common interfering species. The employment of the stable nanocomposite for real sample analysis makes it a deliverable for H₂O₂ sensing.