The Faraday rotation and optical absorption of ferromagnetic Mn 5Ge3 thin films have been measured in the visible and near infrared. Apart from a gradual rise in optical density in the near uv, the absorption is featureless to 2.5 μ. The Faraday rotation behaves similarly. At 500 mμ the room-temperature absorption coefficient α and the 5°K saturation rotation F are 3.5×105 cm-1 and 2.1×105 deg/cm, respectively. The rotation decreases with rising temperature and vanishes at 40°C which agrees well with the bulk Curie temperature of 37°C. The in-plane coercive field Hc decreases monotonically with temperature as Tc is approached. For a 900-Å-thick film Hc is 260 Oe at 0°C. The dependence of magnetic and magneto-optical properties on film structure is discussed. © 1971 The American Institute of Physics.