Nonlinear magneto-optics is the nonlinear optics related to magnetic characteristics. In magnetic media, time-reversal symmetries and axial characteristics of physical quantities must be considered in the description of nonlinear optical phenomena. As a result, it is possible to obtain information of magnetic ordering which is not available by conventional nonlinear optical methods. In this proceeding, the principle of nonlinear magneto-optics and its application to structural analysis and magnetic imaging are given.