Abstract.A magnetically actuated optical phase modulator is described. The phase of a reflected optical beam is modulated by deflecting a Mylar® membrane, coated with a magnetic iron/nickel film, with the field of an electromagnet. A phase change of for light of wavelength 0.633 m was achieved with a driving voltage of only 4 V, much smaller than the voltage required for comparable, electrostaticallyactuated devices. The modulator can be scaled to micron dimensions for fabrication in arrays, scaled for even lower drive voltage, and operated at megahertz frequencies.