MEMS resonator exhibits extraordinary high sensitivity when used as bio-chemical sensor for detecting weight of specimen, adsorption of molecules, etc. by resonant frequency shift, in which piezoelectric transduction is effective to reduce power consumption for portable applications. However, the sensitivity is deteriorated by piezoelectric film due to its energy dissipation. This paper reviews our recent developed piezoelectric MEMS resonators, including cantilever actuated by PZT and detected by piezoresistive gauge, beam resonator actuated by PZT and detected by electrostatic sensor, disk/ring resonator actuated and detected by PZT, for the pursuit of high Q-factor, high resonant frequency, and better device sensitivity. The performance of each device was evaluated and investigated. The advantageous and weaknesses of above devices were discussed for application as bio-chemical sensors.