The bismuth oxide thin films were prepared by thermal oxidation (in air) of vacuum evaporated bismuth thin film on glass and alumina. Surface morphology shows granular structure on glass and triangular shaped grains on alumina substrates. The effect of bismuth oxide thin film overlay of different thickness on Ag thick film microstrip rectangular patch antenna was investigated in the X- band (8-12GHz). The change in the resonance frequency, amplitude, band width, quality factor and input impedance of the antenna were studied. Using the resonance frequency the permittivity and conductivity of bismuth oxide thin film was also measured. Thickness and oxidation temperature of Bi2O3 thin film overlay dependent changes in the patch antenna characteristics was obtained. The input impedance increases due to the overlay. The dielectric constant of bismuth oxide thin film on both substrate calculated from shift in resonance frequency shows thickness and oxidation temperature dependent values. The microwave permittivity and conductivity of Bi2O3 thin film on glass as well as alumina substrate have been reported for the first time using overlay on thick film patch antenna. Thickness of overlay dependent tuning of the antenna has been achieved
