The degradation of two sulfonylurea (Sus) herbicides, cinosulfuron and triasulfuron, has been investigated in aqueous solutions containing TiO2 suspensions as photocatalyst. Cinosulfuron and triasulfuron have been rapidly transformed with different kinetic orders (1 and 1/2, respectively). The calculated quantum efficiencies (phi) of both Sus have been found similar (0.73%). Intermediate products were identified using HPLC-UV or HPLC-MS analyses. A photocatalytic degradation pathway has been proposed, leading to cyanuric acid as a final product. This molecule is known as resistant to all oxidation technologies.