The aim of this research was to study the desulfurization of waste tire pyrolysis oil via photo-oxidation catalyzed by titanium dioxide (TiO₂ or Degussa P-25) at mild reaction condition. The starting waste tire pyrolysis oil contained 0.84 wt% of sulfur content. The photo-oxidation of the pyrolysis oil was carried out by using a 400 W of high-pressure mercury lamp for 1-7 h. The oxidized sulfur compounds were then removed into the extracting phase. The effects of TiO₂ content (1-7 g/L), TiO₂-calcination temperature (400-800℃), reaction temperature (30-70℃), pyrolysis oil/extracting solvent (1/1-1/5 (v/v)), type of extracting solvent (distilled water, methanol and acetonitrile), air flow rate (0-150 mL/min) hydrogen peroxide concentration (0-30 wt%) and stages of the reaction (1-3 stages) on the %sulfur removal were also investigated. The maximum %sulfur removal at 47.5% was achieved when 7 g/L of uncalcined TiO₂ was loaded into the system containing 1/4 (v/v) of pyrolysis oil/acetonitrile at 50℃ for 7 h after 3 stages of reaction. The oxidation of sulfurous compounds in the pyrolysis oil before and after photocatalytic desulfurization was detected by using gas chromatography equipped with a flame photometric detector (FPD) and high performance liquid chromatography (HPLC). The results indicated that the photocatalytic desulfurization using TiO₂ was effective to reduce the sulfurous compounds in the pyrolysis oil; especially, benzothiophenes by converting to sulfones or sulfoxides with higher polarity which was easier to be dissolved into the extracting phase.