The microwave dielectric characteristics of MNb2O6 compounds which are subcomponents of the complex perovskite A(B-1/3’B-2/3")O-3 have been investigated as a function of M ions. All MNb2O6 compounds have the columbite structure. Dielectric properties such as permittivity, dielectric loss, and temperature coefficient of resonant frequency are found to correlate strongly with the M ions. In particular, the temperature coefficient of the resonant frequency may be correlated to the unit-cell volume of MNb2O6. Among these compounds, ZnNb2O6 had very high quality factors.