Ferrite is popular as a core material for RF transformers. Since transmission characteristics of RF transformers are affected by the core’s permeability, which has a large temperature dependence, the development of a method for measuring the core permeability temperature profile is important. In this study, a temperature profile measurement of ferrite core permeability has been investigated using a microstrip line method which has the advantage of the circuit being compact in size and therefore suitable for measuring temperature profiles. Based on the results measured with a sample ferrite core, the temperature dependence of RF transformer performance (isolation) is also discussed. Furthermore, basic results of experiments to compensate for the degradation in isolation is presented.