Nanoparticulate gold catalysts (NPGCs) supported on niobium oxides (Nb2O5) were prepared by different deposition methods. Au nanoparticles (NPs) with a mean diameter of approximately 5 nm were deposited by conventional deposition methods, which include the deposition‐precipitation (DP) and deposition‐reduction (DR) methods, on layered‐type Nb2O5 that possesses a deformed orthorhombic structure. Moreover, Au NPs with a mean diameter of approximately 2.7 nm could be deposited by the sol immobilization method on several crystalline forms of Nb2O5 (deformed orthorhombic, pseudohexagonal, and orthorhombic). NPGCs deposited on deformed orthorhombic Nb2O5 had a higher catalytic activity for CO oxidation. The temperature for 50 % CO conversion was 11 °C for 1 wt % Au/Nb2O5 (deformed orthorhombic) prepared by the sol immobilization method, and the CO conversion was 91 % at 28 °C. As far as we know, this is the first report of highly active Au NPGCs (smaller than 3 nm in diameter) supported on Nb2O5. NPGCs supported on acidic metal oxides will expand the utilization of gold catalysts for new applications.