The dielectric properties of free-standing diamond films grown by the dc arc-jet plasma method are measured by an impedance analyser in the temperature range of 298-573K and at frequencies between 1000Hz and 1 MHz.In the temperature and frequency ranges, the loss tangent can be expressed as a function of temperature and frequency. The loss tangent increases slightly with increasing temperature and frequency. The dielectric properties of the diamond films decrease with the increasing deposited temperature. The structure and quality of diamond films have been analysed by scanning electron microscopy, x-ray diffraction and Raman spectroscopy.