The development of green preparation methods for acidic metal oxide supported gold catalysts is of great importance for the extensive use of gold catalysts as well as for a comprehensive understanding of gold catalysts. In this study, poly(N-vinylpyrrolidone) (PVP) was used as the stabilizer of gold colloids to deposit gold nanoparticles on an acidic metal oxide, Nb2O5. The effects of the PVP ligand on the preparation of Au(-PVP)/Nb2O5 and on the catalytic activities for gas-phase CO oxidation and liquid-phase furfural oxidation were investigated. As removing more ligand PVP of Au(-PVP)/Nb2O5, the catalytic activities for both CO oxidation and furfural oxidation increased. The optimal calcination temperature for Au(-PVP)/Nb2O5 was determined to be 400 °C, and calcination at that temperature gave gold nanoparticles with an average size of 6.4 ± 2.5 nm and of the support of Nb2O5 remained as the original crystalline structure. The temperature for 50% CO conversion (T50%) of Au(-PVP)/Nb2O5 (calcined at 400 °C) was 81 °C. In addition, Au(-PVP)/Nb2O5 (calcined at 400 °C) presented 43% furfural conversion with 100% selectivity of furoic acid under a mild conditions (0.5 MPa O2, 40 °C) in the batch system. These results suggested that Au(-PVP)/Nb2O5 is a good catalyst for both gas-phase and liquid-phase reactions.