The photocatalytic degradation of crystal violet (CV), which is a cationic triphenyl methane dye in aqueous solution has been investigated with colloidal suspension of Au doped TiO2 under both UV and visible light irradiation and compared with undoped TiO2. The degradation has been studied by UV-visible absorption spectroscopy and it is found that Au doped TiO2 is highly efficient for the dye degradation. Doped and undoped titanium dioxide (TiO2) nanoparticles have been prepared as a colloidal suspension using sol-gel hydrolysis method and are characterized by XRD, TEM, and UV-visible absorption spectroscopy. The UV-visible absorption spectra reveal that the intensity of the characteristic peaks of CV diminish with time and within an hour the intensity drop below 3/4th of the maximum intensity and there is concomitant oxidative degradation of the dye. This process is accelerated under UV exposure.