In this paper we have introduced several types of ferroelectric and antiferroelectric thin (thickness <1 m) and thick (thickness >1 mum) films developed in our group for sensor, actuator and transducer applications in microelectromechanical systems (MEMS). Ferroelectric lead zirconate titanate (PZT) films of up to 12 mum in thickness have been prepared on Pt-buffered silicon substrates, which allows for the conventional, through-thickness polarization, and of up to 5 mum in thickness on insulating layer (ZrO2) passivated silicon substrates, which allows for the novel, in-plane polarization. The in-plane poled films make it possible to develop d(33)-mode rather than d(31)-mode bending devices, which immediately leads to two-times improvement in device performance because d(33) approximate to 2 d(31). It also can greatly increase the voltage sensitivity of bending devices because the film thickness and electrode spacing are separated as independent variables, and thus, smaller film capacitance can be obtained by using wider electrode spacing even for fixed film thickness. In addition to PZT ferroelectric films, we have also developed antiferroelectric films as an alternative for high-strain microactuators. The strain level of the antiferroelectric films can reach more than 0.4%, and both digital and analog actuation can be realized by modifying the compositions of the films. As an example for MEMS applications, micromachined, unimorph-type two-dimensional transducer arrays have been fabricated based on both the through-thickness and in-plane polarized PZT films, which can be used for miniaturized, high-resolution acoustic imaging such as hand-held diver's sonar system, medical ultrasound imaging, and non-destructive testing.