The design and construction of an apparatus for domain observation and for the measurement of magneto‐optic rotation and coercivity of thin magnetic films, by means of the Faraday effect, are described. A spatial resolution of 5 &mgr; is achieved, allowing scanning of magneto‐optic properties across the film. Gas flow cooling and heating of the samples result in a temperature range of −120 to +200°C. A special sampling detector allows continuous recording of magneto‐optic rotation and coercivity as a function of temperature and wavelength.