The photocatalytic reduction of NO by CO over a MoO₃/SiO₂ catalyst (2.5 wt% of Mo), which proceeds under UV irradiation at room temperature, is reported for the first time. N₂ and CO₂ are found to be the major reaction products, and the selectivity of the photoreduction is close to 100%. After completion of photoconversion of a NO-CO mixture and brief evacuation at room temperature, a new portion of the NO-CO mixture admitted to the catalyst can be converted with the same rate as during the first irradiation. It is shown that MoO₃/SiO₂ is an inefficient catalyst for the thermal NO reduction by CO, since heating of a NO-CO mixture at 400 and 500°C yields only small amounts of N₂ and CO₂. A reaction mechanism for the photocatalytic NO reduction by CO over MoO₃/SiO₂ is proposed and discussed.