A Micro-electro-mechanical System(MEMS) fiber-optic magnetic sensor based on a MEMS torsional mirror was proposed and a dual-fiber collimator was used for measuring the tiny angle of torsional mirror. The MEMS fiber-optic magnetic senor is consists of a MEMS torsional mirror, a magnetic film and a dual fiber collimator. The mechanisms of magnetic sensing and optical detection of the device were described, and the design and optimization of the device were discussed. A prototype for the MEMS magnetic sensor with a volume of 3.7 mm×2.7 mm×0.5 mm was fabricated successfully by MEMS technologies. The measured output values of the magnetic sensor are consistent with theoretical values. Experimental results indicate that the sensitivity of the magnetic sensor is 0.65 dB/mT. and its minimum resolution magnetic field is 167 nT. The MEMS fiber-optic magnetic sensor combines fiber-optic measurement and compact MEMS structure, and it has advantages of compact construct and simple fabrication processes. Moreover, it can operate without current excitation.