In this work, errors in a ferrite core permeability dispersion measurement using a microstrip line (MSL) method, where three kinds of MSL circuits are used, are evaluated by both an electromagnetic simulation technique and experiments. The computer simulated results have shown that although the measurement errors decrease according to the diameter of the winding wire which passes through a sample ferrite core becomes larger, that is the spacing between the wire and the core gets narrower, a certain amount of error still remains. In order to overcome this problem and improve the measurement accuracy, a metal pipe electrically connected to a ground plane for shielding is placed around the wire of the non-magnetic core circuit which is one of the three MSL circuits noted above.