Taking into account the nonlinear properties of ferrites the output voltage of toroidal transformer with magnetically soft ferrite core is calculated. Calculations are based on methods analogous to those used in nonlinear optics. Initially demagnetized ferrite is assumed to be isotropic. At this condition apart from the harmonic on fundamental frequency the output voltage of transformer contains also higher harmonics of odd order. Nonlinear susceptibilities of third and fifth order are used in calculations Magnetic losses are taken into account considering linear and nonlinear susceptibilities as being complex. These losses affect amplitudes of harmonics in the output voltage of transformer and create phase shifts between components of magnetization on different frequencies in the core and the intensity of exciting harmonic magnetic field. Results obtained in calculations are confirmed by experimental measurement of output voltage of toroidal transformer with MnZn ferrite core. In order to calculate amplitudes of harmonics in the output voltage of transformer numerical values of susceptibilities in question should be known.