Silicon substrates have optical and mechanical properties that provide excellent opportunities for fiber optic sensors. The microbeam forms a structure that functions as an optomechanical modulator. Modulated light can be use to excite the microbeam into resonance. The measured value (such as pressure) causes the deformation of the substrate and, consequently, varies the resonance frequency of the fundamental flexural mode through the intrinsic tension in the microbeam. When the beam vibrates, the incident light is modulated and the reflected light is used to sense vibration of the beam. Microbeams attached to the substrate at both ends are highly strain sensitive and form the basis of a variety of sensors, including pressure sensors, accelerometers, strain, vibration, and temperature sensors. In this paper, the problems in measuring the vibration of microbeams are analyzed. A modulated light from a laser diode has been used to excite the microbeam into vibration. The vibration of the microbeam is measured by using a laser interferometric method. The test results suggest that this method can be used for precision measurement of microbeams.