This paper presents the first fabricated dual-band uncooled resistive infrared thermal microbolometer implemented with a resistive microbolometer and a tunable micro-mirror structure. Tunable reflective micro-mirrors are suspended underneath the suspended resistive microbolometers having a 35 mu m pixel pitch, and they are switched between two positions by the application of an electrostatic force for obtaining different responses in two wavelength infrared atmospheric windows, namely the 3-5 and 8-14 mu m, by tuning the optical tunable resonant cavity. This approach allows assessing the actual temperature of the viewed scene by comparing the responses of the detector in these two wavelength infrared atmospheric windows. The absorption coefficients of the detector are simulated by using the Cascaded Transmission Line (CTL) model, and the sacrificial layer thicknesses are optimized to obtain maximum absorption from these two wavelength regions. The absorption coefficients obtained from the measurements are in correspondence with the simulations. The responsivity measurements results shows that the absorption is decreased in an amount of 17.9 % in the 3-5 mu m spectral band, while the absorption is increased in an amount of 8.5 % in the 8-14 mu m spectral band, depending on the micro-mirror position. These initial results are promising for the dual-band detection using uncooled infrared microbolometer detectors.