High-frequency magnetic cores are being used in different applications, from low-power electronic devices, up to high-power components. For different material types it is required to identify material-specific equivalent circuit in order to simulate its behaviour in wide frequency range. This presentation describes a method for obtaining such an equivalent circuit with the use of a rational function in the s-domain such as it represents the material frequency characteristics. For the method presentation, the measured data obtained for a real magnetic core was used.