The performances of a visible light active structured photocatalyst in the oxidation of arsenite to arsenate in aqueous solution were investigated. In particular, the photocatalytic active phase was Cu-doped ZnO, while polystyrene (PS) pellets were used as support. The Cu-doped ZnO photocatalyst was immobilized on polystyrene pellets surface by "solvent casting method" and characterized by different techniques. The photocatalytic tests were performed in a floating bed reactor using a visible LEDs strip as light source. The complete As(III) oxidation was achieved after 120 min of visible irradiation at a Cu-doped ZnO loading on polystyrene pellets equal to 5 wt %. Furthermore, the optimized photocatalyst was reused for several cycles without any substantial decrease of photocatalytic performances. In order to determine which reactive species plays a more significant role in the oxidation of As(III), the effects of different radical scavengers were tested. The results evidenced that OH center dot and O-2(center dot-) seem not to be the main oxidant for the direct As(III) oxidation, whereas the oxidation mechanism of As (III) using Cu-doped ZnO structure photocatalyst seems to be related to the h(+) holes generated under visible light irradiation.