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/TiO₂particles exhibited a mixture structure of anatase and rutile with a particle size below 70 nm; the surface areas of V/TiO₂were large (15.0 m²/g) compared with that of pure(7.0 m²/g). The XRD pattern for V/TiO₂revealed 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/TiO₂had a higher hydrophilic property than did pure TiO₂. In addition, when the vanadium component was added, new Brφnsted 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. Furthennore, the photoactivity of V/TiO₂increased remarkably with H₂O: 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/TiO₂relative to that in pure TiO₂.