Two kinds of nano-CeO₂-supported low loading Ru catalysts were prepared by ultrasonic-assisted incipient wetness impregnation method and their applications in catalytic wet air oxidation (CWAO) of butyric acid (BA) were investigated. Both of the catalysts were characterized by XRD, XPS, TEM, N₂ adsorption–desorption, Raman and H₂-TPR. According to the characterization results, compared to Ru/CeO₂ catalyst, the active component was well dispersed on the support and the particle sizes were smaller for the Ru/CeO₂-A catalyst which was added to some absolute ethanol in the process of preparation. Meanwhile, Ru/CeO₂-A catalysts possessed a high active surface area and had a higher Ce³⁺ and oxygen vacancy content due to the strong interaction between Ru species and CeO₂. Therefore, the Ru/CeO₂-A catalyst presented higher catalytic activity and the chemical oxygen demand (COD) removal can increase up to 64.05% after 2 h. It had excellent stability and can be reused many times without obvious loss of activity.