TiO₂ is the most widely used photocatalyst for the decomposition of various organic pollutants because of its high activity, chemical stability, low price, and nontoxicity. Doping TiO₂ with transition metal ions has been frequently attempted to extend the spectral response of TiO₂ into visible region since pure TiO₂ requires near UV light absorption because of its wide band gap of 3.2 eV. In this research, the effect of co-doping metal ions such as Platinum (Pt), Chromium (Cr), and Vanadium (V) in TiO₂ which separately shows visible-light photoactivity have been investigated in an attempt to enhance the photocatalytic activity under visible light irradiation. Pt-Cr-, Pt-V-, and Cr-V- co-doped TiO₂ samples were successfully synthesized by sol-gel methods and studied by means of X-ray diffraction, UV-Vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. Photocatalytic activities were demonstrated for the degradation of Methylene Blue (MB), phenol and the oxidation of iodide in aqueous solution under visible light irradiation at wavelengths > 400 nm. Co-doped TiO₂ with 0.3 % Pt and 0.3% Cr showed better photocatalytic activity in both MB degradation and oxidation of iodide than separately doped, whereas reaction rates of MB degradation and I- oxidation decreased in co-doped TiO₂ with 0.3% Pt and 0.3% V. Co-doped TiO₂ with V and Cr also showed good activity for the oxidation of iodide to tri-iodide. However, for the degradation of phenol, all co-doped TiO₂ samples didn’t show significantly enhanced photocatalytic under visible light irradiation compared to their single doped counterparts.