This study aimed to prove the promotion effects of ultrasonic on malachite green (MG) decolorization in the ultrasonic-assisted ozone oxidation process (UAOOP), and propose the possible pathway of MG degradation. The decolorization of MG followed an apparent pseudo first-order kinetic law (initial MG concentration 100-1000 mg/L). When ultrasonic (US) was applied with ozone simultaneously, the apparent pseudo-first-order rate constant (K-app) increased, and the time MG decolorized to the half of initial concentration (T-1/2) shortened 185s (1000 mg/L). Moreover, the stoichiometric ratio (Z(app)) between O-3 and MG was enhanced by US to 2.0 mol, saving 11% oxidant addition, comparing to individual ozone process. These results indicated that the application of US can reduce reaction time and dose of ozone addition. The possible pathway of MG degradation included three major approaches. And the result suggested that the reaction between MG and hydroxyl radical was substitution reaction rather than adduct reaction. (C) 2012 Elsevier Ltd. All rights reserved.