In this paper, we prepared high-quality ZnO thin films for application of FBAR (Film Bulk Acoustic Resonator) by using pulse DC magnetron sputtering. To prevent the formation of low dielectric layers between metal and piezoelectric layer, Ru film of 30 nm thickness was used as a buffer layer. In addition we investigated the influence of annealing condition with various temperatures. As the annealing temperature increased, the crystalline orientation with the preference of (002) c-axis and resistance properties improved. The single resonator which was fabricated at $500^{circ}C$ exhibited the resonance frequency and the return loss 0.99 GHz and 15 dB, respectively. This work demonstrates potential feasibility for the use of thin film Ru buffer layers and the optimization of annealing condition.