Visible light-excited ethanol dehydration reaction steps to adsorb ethanol and then to donate an electron to transform Vandium(IV) to V(III) site exposed on mesoporous V(IV)-TiO2 catalyst were successfully monitored by means of V K beta5,2-selecting XANES spectroscopy. Spherically-bent Germanium(422) crystal was used for the X-ray fluorescence analyses and Xe arc lamp of 500W was illuminated at 10 mm apart from catalyst samples under on reaction conditions. Specific redox reaction mechanism between V(IV) and V(III) states was proposed for dehydration reaction over the mesoporous V-TiO2 catalyst based on the V K beta5,2-selecting XANES compared to general vanadium catalysts starting from V(V) state for dehydrogenation reaction.