A novel optical excitation and detection apparatus was used to investigate the characteristics of silicon micro-resonators, which was activated into vibration by a laser beam irradiation. The beam diameter of the excitation light was less than 10 'mu'm. The vibration amplitude of the resonator was detected by the interferometer with high resolution of 0.1 nm and measurement repeatability of less than 3 nm. The resonant frequency of the micro-resonator was obtained to be 8.75 kHz with full-width at half-maximum (FWHM) of 0.18 kHz. It is shown that the method is useful and reliable for measuring micro-displacement and micro-vibration of minute objects with nanometer accuracy.