This short paper deals with the modes of the dielectric post resonator when epsilonr is large. The normalized frequency F0 = (pi D/lambda0) √ as a function of D/L is discussed. The simple approximate expressions for the resonant frequencies of the lower order modes are given. The properties of the TE011, mode are discussed in detail from the point of view of its application to the measurement of the complex permittivity of microwave dielectrics. Curves and expressions for fast and simple determination of the maximum measurement errors are given.