Synthesis temperature is always playing a crucial role on the determination of dielectric properties of materials. In this letter, (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 (BZN) thin film was deposited onto quartz glass substrate by RF magnetron sputtering at room temperature and then post-annealed using rapid thermal processing. Film has been characterized with respect to crystalline phase and surface morphology, by means of X-ray diffraction and atomic force microscopy, suggesting no crystalline structure exists in annealed BZN film after post-annealing. Microwave dielectric properties were measured by split post dielectric resonator technique. After annealing at 150 °C, film showed excellent dielectric permittivity and low loss in microwave frequency range. This result indicates that the annealed BZN thin film has a great potential to be alternative of microwave materials fabricated at low temperature.