N-Nitrosodimethylamine (NDMA) contamination has become an issue since trace levels of NDMA have been observed in drinking water in California and Canada. NDMA, which is generated during water treatment as a disinfection byproduct (DBP), is known to be highly carcinogenic and resistant to biodegradation in the aquatic environment. Several advanced technologies such as ozonation, Fenton’s Reagent oxidation, and reduction by zerovalent iron have been employed to remove NDMA. In this research, we synthesized metal-doped TiO₂ such as platinum (Pt), chromium (Cr) by sol-gel methods and investigated the photocatalytic degradation of NDMA in aqueous solution under visible light irradiation > 420 nm. In aqueous suspensions, NDMA was degraded with 0.3% Platinum (IV)-doped TiO₂ under illumination at wavelengths > 420 nm whereas commercial TiO₂ (Degussa P-25) did not show significant degradation of NDMA under visible light irradiation. Under UV light irradiation > 300 nm, Pt(IV)-doped TiO₂ showed higher photocatalytic activity for NDMA degradation than un-doped TiO₂ over a wider pH range. In addition, the degradation rates were enhanced with Pt metal deposition on the TiO₂ particle surfaces. The effects of doping concentration, calcination temperature, oxidation states, and pH on the photocatalytic degradation of NDMA were determined. The clearly identified degradation products give insight into the mechanism of oxidation under visible light irradiation.