The object of this document is to describe a measurement method of dielectric properties in the planer direction of dielectric plate at microwave frequency. This method is called a cavity resonator method. It has been created in order to develop new materials and to design microwave active and passive devices for which standardization of measurement methods of material properties is more and more important. This method has the following characteristics: . the relative permittivity ?à ' and loss tangent tan? values of a dielectric plate sample can be measured accurately and nondestructively; . temperature dependence of complex permittivity can be measured; . the measurement accuracy is within 0,3% for ' and within 5X10-6 for tan ; . fringing effect is corrected using correction charts calculated on the basis of rigorous analysis. This method is applicable for the measurements on the following condition: Frequency : 2 GHz f 40 GHz; Relative permittivity : 2 ' 100; Loss tangent : 10-6 tan 10-2.