The photocatalytic degradation of formetanate (FMT) was studied using titania Degussa P-25 as a catalyst. The disappearance of formetanate was proved to follow a half-order kinetics. This implies that two active sites are involved in the adsorption of one molecule of formetanate (dissociative adsorption). In our conditions, complete mineralization of 20 ppm of pure formetanate occurred within 125 min of UV-radiation. The presence of (i) formulation agents and (ii) of humic acids seemed to have an inhibiting effect on the initial rate. In all cases, mineralization of FMT led to a greater percentage of ammonium than of nitrate. Photocatalysis proved to be an excellent new advanced oxidation technology (AOT) to eliminate formetanate residues present in real surface and ground waters.