A force microscope is described which uses a fiber-optic interferometer as the cantilever displacement sensor. Low thermal drift and reduced susceptibility to laser frequency variation are achieved due to the small (several micrometer) size of the interferometer cavity. A sensitivity of 1.7×10-4 Å/√Hz1/2 is observed for frequencies above 2 kHz. The drift rate of the sensor is on the order of 3 Å/min. As an initial demonstration, laser-written magnetic domains in a thin film sample of TbFeCo were imaged.