AbstractThe aim of this work was to improve photo‐catalytic activities of zinc oxide thin films for the degradation of methyl orange (MO) using a new approach based on the combined effect of lanthanum doping and porous substrate of silicon (Psi). Therefore, undoped and lanthanum‐doped zinc oxide thin films (ZnO : La) were deposited on porous silicon substrate (PSi) by spin coating chemical deposition. Studies of the photo‐catalytic activity showed that the La (25 %)‐doped ZnO layer exhibited an improved photocatalytic performance in the degradation of methyl orange. Around 91.53 % and 70 % of the MO degradation was achieved within 180 min under illumination with UV and visible light respectively, suggesting that La‐doped ZnO films deposited on Psi substrate are favorable candidates to enhance the photo‐degradation of methyl orange.