This study focuses on the removal of methyl orange (sodium p-dimethylaminoazobenzene sulfonate), a representative dye compound, in a liquid photo-system using nanometer-sized V/TiO2synthesized by commercial sol-gel method. The V/TiO2 particles exhibited a mixture structure of anatase and rutile with a particle size below 70 nm; the surface areas of V/TiO2 were large (15.0 m2/g) compared with that of pure TiO2(7.0 m2/g). The XRD pattern for V/TiO2 revealed that the vanadium component was substituted well into the titanium ion sites until it reached an amount of 5.0 wt%. The XPS result confirmed that V/TiO2 had a higher hydrophilic property than did pure TiO2. In addition, when the vanadium component was added, new Bronsted acid sites were generated. Based on these results, the photodecomposition of methyl orange in liquid reaction was enhanced over V/TiO2 when compared to that over pure TiO2, especially when using the 5.0 wt% vanadium addition sample. Furthermore, the photoactivity of V/TiO2 increased remarkably with H2O2 addition in an aqueous solution. From ion chromatogram data, NO2-, NO3-, Co3 2-, and SO4 2- ions appeared as products of the methyl orange photodegradation. From the results, it could be suggested that complete photo-oxidation dominated in V/TiO2 relative to that in pure TiO2.