This paper presents a kind of flexible ultrasonic transducer, which consists of bottom electrode, ZnO piezoelectric thin film, top electrode and pliable polyimide substrate. The top and bottom electrodes are fabricated by DC magnetron sputtering, and ZnO piezoelectric layer is deposited by the reactive RF magnetron sputtering. The adhesion between layers is robust which makes the device perfectly flexible. SEM and XRD results show that the piezoelectric film exhibits a columnar structure with highly (002) preferred orientation and the film thickness is of 4~8 μm. The average grain size and mean intrinsic stress levels are calculated from XRD results. The results show that the average grain size is a bout 22 nm, with intrinsic stress of -1.248 4 GPa. The resonant frequency measured by laser Doppler vibrometer is around 5 MHz. Meanwhile, the investigation shows that the thicker ZnO film has great amplitude, resulting Qvalue to increase.