Аннотация:The Faraday effect in the rhombohedral weak ferromagnetic FeBO3, which is due to the magnetization component parallel to the C3 axis of the crystal, is experimentally observed for the first time. The Faraday effect due to component mz with aperiod of 120 deg. at the rotation of the sample around C3 axis was found in both samples 5 and 8 µmthick. The experimental points are approximated bya sinusoid.