Microelectromechanical systems (MEMS) technology has been used to fabricate miniature acoustic transducers for a variety of applications in different media and frequency ranges. The consistency in performance of individual transducer afforded by batch-fabrication also makes it feasible to employ MEMS transducer arrays in beam forming or beam steering technique. This paper will first introduce our own research work on micromachining of piezoelectric acoustic transducers, including sol–gel thin film piezoelectric microphone for audio application; composite thick film piezoelectric micromachined ultrasonic transducer array for biomedical imaging; and transducer arrays fabricated by Si-PZT bonding technology for hydrophone and audio beam applications. The preliminary results on receiving and transmitting performance of the fabricated transducers and arrays will also be reported. In addition, a scanning acousto-optic microscope, which uses a single micromachined acousto-optic sensor and interferometry, will also be introduced. With this technique, it is possible to map a spatial sound field distribution at micrometer resolution.