The gas-phase photooxidation of trichloroethylene (TCE) on Pt/TiO2 has been investigated. The wavelength dependence of this reaction on Pt/TiO2 shows that the addition of small amounts of platinum (≤2%) to TiO2 can enhance the photooxidation of TCE to much longer wavelengths. This result correlates with Maxwell-Garnett calculations and experimental absorption curves for Pt/TiO2 samples. Although the spectral response of Pt/TiO2 extends to longer wavelengths, Pt/TiO2 is found to be less effective in the photooxidation of gas-phase TCE upon broad-band irradiation (λ > 300 nm) compared to TiO2. It is proposed that site blocking by the Pt particles of the most active sites, Ti3+ sites, is the cause of the decreased photoactivity. In addition, it has also been determined that the photoproduct distribution changes as a function of platinum loading. Mechanisms to explain the observed effects of Pt loading on the photooxidation of TCE on Pt/TiO2 are discussed.