In this work, transparent amorphous-MgNb2O6 thin films were fabricated on ITO/glass substrates using the sol–gel method. The change in the chemical states, as well as the optical and dielectric properties of MgNb2O6 films at various annealing temperatures is investigated. In this study, MgNb2O6 films exhibited the amorphous phase when the annealing temperature was below 600°C. From X-ray photoelectron spectroscopy, the major parts of the films' chemical states can be indexed as Mg2+, Nb5+, Nb4+, and O2−. Furthermore, the Nb4+ element can be reduced at higher annealing temperatures. The average transmission percentage in the visible range (λ = 400–800 nm) is over 80% for all MgNb2O6/ITO/glass samples, whereas the optical band gap (Eg) for all samples is estimated at ~4 eV. In addition, the dielectric constant was calculated to be higher than 20 under a 1 MHz AC electric field, with a leakage current density below 2 × 10−7 A/cm2 at 1 V. In this study, the fabrication procedure and experiment results of MgNb2O6 films are introduced for transparent microelectronics.