The dissolution of refractory PuO2 in HNO3-HF-H2O dissolvents was studied. Results showed that increasing either the HNO3 or the HF concentration increases the dissolution rate, and that formation of a Pu(IV) fluoride complex decreases the rate. It was also found that oxidation of dissolved Pu(IV) helps maintain the presence of a fluoride ion as a catalyst and is thus highly beneficial to PuO2 dissolution.