This paper, at first, discuss the availability of a cavity resonance method using the resonance frequencies of some TM0m0 modes in a circular cavity to measure the frequency dependence of a dielectric rod sample. The influence of sample insertion holes to the measurement are estimated accurately on the basis of the rigorous analysis by the Ritz-Galerkin method. Some dielectric rod samples were measured by using two modes TM010 and TM020 hi each of two cavities with different heights. The measurement precision for the relative permittivity was improved within 0.3 %, compared with 3 to 7 % in the perturbation method. Then one of the cavities was set in an environmental test equipment and the temperature dependences of dielectric rod samples were measured. As a result, the present method is useful to measure the frequency and temperature dependences of dielectric rod samples.