Microcantilever beams have been widely used in micro-electromechanical systems (MEMS) devices. Their reliability is an essential factor for a successful MEMS product in an industrial setting. This study discusses the fatigue life of polysilicon microcantilever beams of various dimensions that were subjected to bending by a piezoelectric actuator. Both experimental and analytical results were obtained. A 100-Hz piezoelectric actuator was used to facilitate the test runs with good repeatability of the fatigue load. A finite element-modeling program, ANSYS, was used to investigate the stress distribution on the microcantilever beam. The fatigue life of the specimen was found to lie between and cycles for stress level ranges from 4.07 to 2.31 GPa. The experimental data from this study were incorporated with published references into an S-N curve, which showed that the fatigue life was dependent on both stress and frequency levels of the loading cycles. Low frequency loading was associated with increased sensitivity of fatigue life versus stress level. An empirical correlation was established for predicting fatigue to provide the MEMS designer with a reference for various applications.