This paper describes a free space method for measuring the permittivity at X band and higher frequencies over a wide temperature range. Measurements are limited to values of &egr;′>6 and 10−3<tan&dgr;<0.2. &egr;′ can be determined to 1 or 2% over a significant range; however, for tan&dgr; the range and accuracy are limited. X band measurements are presented for ZrO2at room temperature and Al2O3at room temperature, 1100°C, and 1450°C. Elevated temperature measurements can be performed without heating the microwave components. This method is suitable for use in the millimeter wavelength region. Curves for use in evaluating &egr;′ and tan&dgr; have been previously recorded by the author [``Values for Scattering by Dielectric Spheres in the Region of the First Resonance,'' NRL Report 6365 (30 December 1965)].