Inductive instrument transformers are widely-used to measure currents in the power grid. Harmonics currents increase due to the proliferation of nonlinear equipment in the power grid. At higher frequencies, eddy currents inside the core increase, causing a change of the electrical parameters of the current instrument transformer (CT). For this reason, its frequency response is influenced. To consider this behavior during the design of CTs, this dependency has to be analytical calculated. The general characteristics of CTs can be described using the equivalent circuit of transformer. In this, the behaviors of the core are considered by the magnetizing inductance L m and the iron loss resistance R Fe . Due to magnetization effects and eddy currents, the parameters L m and R Fe are dependent on the magnitude and frequency of the current. In this paper an analytical method is presented to compute the frequency dependent magnetization inductance and iron losses resistance of the conventional equivalent circuit of CTs.