An expression for high-frequency susceptibility of a ferroelectric material in a constant magnetic fieldH0parallel to the direction of spontaneous polarizationP0has been derived. The reflection and transmission of light through the ferroelectric is considered for the normal incidence at the surface (along the normal&ngr;&vec;to the surface). It is shown that the polarization plane in reflected light should be rotated through an angle proportional to the productP0H0.ForH0⊥&ngr;&vec;,the angle of rotation of the polarization plane of transmitted light is a periodic function of the optical path, its amplitude being proportional toP0H0.In theH0‖&ngr;&vec;geometry, a weak gyration effect proportional toP0H0is observed in transmitted light, in addition to the Faraday effect. This effect does not depend on the optical path, and is canceled during backward transmission, in contrast with the Faraday effect. The effect is apparently similar to “magnetopolarization gyration,” but the estimates give a much smaller magnitude of the effect. The above magnetooptical effects can be observed not only in ferroelectric crystals of any symmetry, but also in insulators in constant electric and magnetic fields. ©1997 American Institute of Physics.