This paper describes a method for measuring magnetic permeability dispersion of ferrite cores widely used in RF devices such as splitters in CATV systems. The present method has a step of measuring reflection coefficients for three kinds of microstrip line circuits, one having a test sample (ferrite core) mounted on it, one with a non-magnetic core instead of the ferrite, and one with an impedance matching resistor only. From the three reflection coefficients derived, the impedances of the coils with the ferrite and non-magnetic cores, respectively, are calculated and the complex permeability is determined by dividing the impedance of the ferrite core coil by the reactance component of the non-magnetic core coil. In this paper, the accuracy of the proposed method is discussed through a electromagnetic simulation and then the calculated results are compared with the experiments, indicating the validity of the method.