Abstract:A technique is analysed for the determination of complex permittivity of MIC substrates for deposition of high- superconducting (HTS) thin films. By using high Q factor TM circular cavity, several monocrystals which are often used for deposition of HTS thin films are measured. The results show that the technique covers accurate measurements of the low-loww monocrystal and isotropy dielectric materials at different temperature, and the test is simple, rapid and automatic, and some directional complex permittivity of the dielectric materials can be measured.