In this study, we have proposed a novel laterally driven piezoelectric MEMS (MicroElectro Mechanical Systems) switch using a high-aspect-ratio (AR) PZT (Pb[Zr xTi 1-x]O 3) structure. Then, the fabrication process of the PZT structure based on PZT filling process in a deep Si trench is developed to realize a laterally driven PZT microactuator. At first, the process of the Si trench with a thin Al 2O 3 layer as a Pb-diffusion barrier layer and with a Pt film as the electrode for the actuator is successfully developed. Then, it is demonstrated that the dense and crack-free PZT structure with high-AR can be fabricated by the PZT filling process in the Si trench by nanocomposite sol-gel method. In addition, it is speculated from the X-ray diffraction pattern that the composite PZT has pure perovskite phase and piezoelectric property. The remnant polarization (P r) and the coercive field (E c) of a nanocomposite PZT thick film measured 11.7 μC/cm 2 and 71.2 kV/cm, respectively. As the result of these experiments, it is demonstrated that the fabrication process of the high-AR PZT structure has the potential to realize the laterally driven piezoelectric MEMS switch.