Mg and Ca niobate columbite (MgNb₂O₆ and CaNb₂O₆) were synthesized via hydrothermal reaction and post-heating process. In the CaNb₂O₆, the distortion degree of NbO₆ octahedra is larger than that in the MgNb₂O₆, and the distortion probably provides a smaller band gap. The Ag deposition was carried out by the reduction of Ag⁺ cation by ultraviolet radiation for both columbites, and the Ag metal can be deposited on only CaNb₂O₆ because of the smaller band gap of the CaNb₂O₆. Synchrotron XRD and XAFS confirm that Ag⁺ cation was not exchanged for Mg and Ca during the deposition treatment. The Ag⁺ cation was reduced to deposit on the CaNb₂O₆ with 4.5 nm in size. The deposited Ag nanoparticles show the surface plasmon resonance which can assist in photocatalytic reaction. For phenol degradation, the reactivity was accelerated by the deposit of Ag metal nanoparticles on CaNb₂O₆ in this research. The Ag deposition also gave some antibacterial activity.