Effect of surface acid properties of HNO3 and NaOH modified VOx/Al2O3 catalysts on methanol selective oxidation was studied by solid-state nuclear magnetic resonance and X-ray powder diffraction (XRD) spectroscopy. The surface acidity including type and strength of the acid sites in the catalysts was characterized by the adsorption of probe molecules. Compared with the VOx/Al2O3 catalyst, stronger Bronsted acid sites on the acid-treated VOx/Al2O3 catalyst lead to higher selectivity for DMM, while the base-treated VOx/Al2O3 catalyst with no Bronsted acid site gives rise to formate instead of DMM. Proposed mechanism for methanol oxidation reaction over the VOx/Al2O3 catalysts. Methanol selective oxidation over VOx/Al2O3 catalysts with different surface acidity was studied. The XRD experimental results show that the bulk structure of the catalysts did not been changed by the acid or base modification. A significant selectivity to the reaction products as a function of the acid properties of the catalysts was observed. Comparing to the VOx/Al2O3 catalyst, stronger Bronsted acid site on the acid-treated VOx/Al2O3 catalyst leads to higher selectivity for dimethoxymethane, while the base-treated VOx/Al2O3 catalyst with no acid site gives rise to formate instead of dimethoxymethane.