Surface properties of nanoceria can strongly affect the catalytic performance in oxidation reactions. In this work, a simple but efficient post-treatment, where H2O2 is used as a complexing agent to dissolve Ce3+ from the surface of CeO2 nanorods with the help of ultrasonic treatment, is carried out to tune the surface properties and increase their catalytic performance for catalytic wet air oxidation (CWAO) of phenol. It is found that the dissolution of Ce3+ from the surface of CeO2 nanorods can create more surface defects and result in a much rougher surface. The H2O2-ultrasonic treatment can also increase Ce3+ concentration, create more surface oxygen vacancies, and narrow the band gap of CeO2 nanorods. These properties enable H2O2-ultrasonic-treated CeO2 nanorods (CeO2-H2O2-sf) to possess strong oxidizing ability to effectively oxidize phenol. Additionally, for the sake of comparison, other post-treatments, including calcination, H2O2, and ultrasonic-H2O, are also imposed on CeO2 nanorods.