The object of this document is to describe a measurement method of dielectric properties inthe planer direction of dielectric plate at microwave frequency. This method is called a cavityresonator method. It has been created in order to develop new materials and to designmicrowave active and passive devices for which standardization of measurement methods ofmaterial properties is more and more important.This method has the following characteristics:. the relative permittivity ' and loss tangent tan values of a dielectric plate sample can bemeasured accurately and nondestructively;. temperature dependence of complex permittivity can be measured;. the measurem