This paper described ultraviolet (UV) radiation sensing using ZnO based Film Bulk Acoustic-wave Resonator (FBAR). The resonant frequency upshifted when there was UV illumination on the FBAR. For 365 nm UV light, the frequency upshift was 9.8 kHz with an intensity of 600 µW/cm2, and the detection limit of the sensor was 6.5 nW. The frequency increase of the FBAR UV sensor was proposed to be due to the density decrease of ZnO film upon UV illumination. When UV was incident on the ZnO film, it can cause oxygen desorption from the ZnO surface, resulting in density decrease of the film. This study has proven the feasibility of detection of low intensity UV using ZnO film based FBAR.