The detailed structures of monomeric ReOxcatalysts supported on the CeO2surface and the reaction mechanism of the deoxydehydration (DODH) reaction were investigated by density functional theory calculations. After examining various ReOxHystructures over CeO2without substrate adsorption, the stable structure under the experimental condition at 400 K was determined to be the ReVIIO2species. The reaction mechanism of DODH was then investigated for the conversion of 1,4-anhydroerythritol to 2,5-dihydrofuran as a model reaction. Through the investigations of several reaction pathways, an oxygen vacancy-assisted mechanism, in which the starting structure is the ReIVO species and the oxidation state of the Re atom changes between +IV and +VI during the reaction, was postulated to be the most plausible pathway, considering the energies of the intermediates and the barrier height for the cleavage of the two C-O bonds.