The Design of Experiment (DoE) technique has been used to investigate the photo-electrochemical removal of diuron (DRN) from wastewater. The process is carried out in a photo-electrochemical flow reactor, in which titania nanotubular electrode is irradiated with a simulated solar light. Different operative conditions have been investigated, in a planned 23 full factorial design in which imposed current density, flow rate and initial concentration have been varied at two levels. The removal process of DRN was investigated in terms of specific removal rate (K) and cell voltage (E), which were assumed as objective functions: the results show that the applied current has a paramount effect on both of the objective functions. From the analyses of the intermediates, it appears that the investigated parameters may exert different effects on the distribution of the reaction products: the initial concentration of diuron and the electrode potential seem to play a more important role, in this case.