Herein, we report a newly developed mesoporous VOx-CeO2 catalyst with dominant monomeric VOx species, which can promote the gas-phase ODH reaction of benzyl alcohol-to-benzaldehyde (BA-to-BAD) by molecular oxygen at a surprisingly low temperature range of 203-243 °C, with a high mass-specific activity of ∼25 mmol·gcat-1·h-1 and TOF of 1367 h-1. To the best of our knowledge, it appears to be the most effective transition metal oxides catalyst for the BA-to-BAD reaction in the gas phase. Experimental measurements and density functional theory (DFT) calculations suggest that the activities of VOx-CeO2 catalysts strongly depend on the polymeric states of surface VOx, with monomeric VOx giving much better performance than bigger VOx clusters. It is important to highlight that a specific monomeric VO3 species, only occurring under the reaction conditions, is identified for the first time to have the key influence on BA oxidation. Moreover, it has been found that the origin for the unique activity of such monomeric VOx-CeO2 can be attributed to its electronic "hole" structure.