An electrically switchable computer-generated hologram (CGH) was fabricated using a liquid crystal (LC) cell. A polymethylmethacrylate (PMMA) film, which was spin-coated on one glass substrate of the LC cell, was patterned by a focused $2\mathrm{Me}\mathrm{V}$ proton beam with a CGH phase pattern ( $2\mathrm{\mu m}$ resolution). With an applied voltage on the LC cell CGH sample, an index modulation was produced between the regions with and without PMMA because of the reorientation of LC molecules under the external electric field. The maximum diffraction efficiency measured was about 28.7%. The operating voltage was below $15{\mathrm{V}}_{\text{rms}}$ .