This study focuses on the relationship between the photocatalytic activity of benzene and the surface properties of nano-sized Al/TiO₂. The results indicate that the Al/TiO₂ particles, which are below 150 nm in size, exhibited a uniformly spherical anatase structure. In terms of surface properties, the 10.0-wt% Al/TiO₂ formed a larger (29.9 m²/g) area compared with that formed by pure TiO₂ (50 m²/g). The XRD pattern for Al/TiO₂ developed a stable anatase structure after thermal treatment at 800℃. On the other hand, pure TiO₂ was rapidly transformed into the rutile type after thermal treatment above 600℃. In addition, the XPS and TG results show that Al/TiO₂ possessed a higher hydrophilic property than did pure TiO₂. The TPR results also reveal that the Ti³⁺ or Ti⁴⁺ in Al/TiO₂ could be more easily reduced to Ti⁰ (which influenced the photoreaction), compared with pure TiO₂. The photodecomposition of benzene was enhanced in Al/TiO₂ compared to pure TiO₂, especially with H₂O addition. The catalytic activities of TiO₂ and 10.0-wt% Al/TiO₂ were almost the same in the plasma system. The conversion to CO₂, however, was slightly enhanced in the case of 10.0-wt% Al/TiO₂. Nonetheless, upon H₂O addition, the conversion to CO₂ using both catalysts increased remarkably. This outcome may be attributed to the presence of the OOH radical in both catalysts, which induced the complete oxidation reaction of benzene in TiO₂ and 10.0-wt% Al/TiO₂. The OOH radical was generated by the reaction of H₂O and O₃ to the stronger light source and plasma level in the system.