Double-shelled GaN hollow spheres are prepared for photocatalytic reduction of CO2 through ammonia-gas nitridation of shape-analogous Ga2O3 hollow spheres. Small amount oxygen in situ doping narrows the bandgap of the GaN hollow sphere which significantly enhances the utilization of visible light. The large surface area of the hollow spheres provides more activity sites for the photoreduction reaction. The specific hollow structure also allows the trapping of the incident light for a longer time during photocatalysis process, which provides more opportunities for light absorption. Loading of Pt and RuO2 cocatalysts further enhances the separation of photogenerated electrons and holes to improve the CO2 reduction activity.