Abstract: The tribological properties of AlCoCrFeNiCu high entropy alloy sliding against GCr15 in hydrogen peroxide with different concentrations were evaluated using a ring-on-block wear test machine. The microstructure and morphology of the worn surfaces were analyzed using scanning electron microscopy (SEM) and the surface components of the tested samples were measured by energy dispersive spectrometer (EDS). The results indicated that the friction coefficient of AlCoCrFeNiCu/GCr15 tended to decrease with increasing concentration of hydrogen peroxide. The wear volume of AlCoCrFeNiCu alloy in hydrogen peroxide was much smaller than that in deionized water. The main wear mechanism was adhesive wear in deionized water, while the friction pair was dominated by a mixture of oxidative wear, abrasive wear and adhesive wear in 30% and 60% H₂O₂. In contrast with that in other concentrations, the wear resistance of AlCoCrFeNiCu alloy in 90% H₂O₂ increased significantly due to the formation of a compact oxide film.