We present an optical fiber voltage sensor by Michelson interferometer employing a Fabry-Perot tunable optical filter and the phase generated carrier demodulation algorithm. By mounting a Michelson interferometer fabricated by an optical fiber coupler on a piezoelectric transducer, a dynamic strain would be generated to change the phase difference of the interferometer when the measured voltage is applied on the piezoelectric. The phase generated carrier demodulation method was used to obtain the phase variation of the interferometer by applying demodulate signal on a Fabry-Perot tunable optical filter. The measured voltage can be obtained by the variation of the phase; the random phase shift in the interferometer and the intensity fluctuation of the light source of the sensor can be eliminated. The experiment results show that the relation between the phase variation and the voltage applied on the piezoelectric is approximately linear. The dielectric reliability of the sensor has been verified according to the IEC standard.Index Terms-Optical fiber voltage sensor, Michelson interferometer, Fabry-Perot tunable optical filter, Phase generated carrier 1530-437X (c)