The columbites MgNb2O6, MgTa2O6, and corundum-type Mg4Nb2O9 ceramics were prepared by the conventional solid-state ceramic route. The structure and microstructure of the sintered samples were investigated by X-ray diffraction and scanning electron microscopic techniques. The microwave dielectric properties of the samples were measured by the resonance method in the frequency range 4–6 GHz. The dielectric properties have been tailored by forming a solid solution between MgNb2O6 and MgTa2O6 and by the substitution of TiO2 for Nb2O5 in both MgNb2O6 and Mg4Nb2O9 ceramics. The Mg(Nb0.7Ta1.3)O6 has r=29, Qu×f=67 800 GHz, and f=0.8 ppm/°C and the MgO–(0.4)Nb2O5–(1.5)TiO2 composition has r=34.5, Qu×f=81 300 GHz, and f=−2 ppm/°C.