A novel thin film transformer based on double sided YBa 2 Cu 3 O 7−x (YBCO) thin films with high operating performance, named a high temperature superconducting thin film transformer (HTS-TFT), is proposed and tested. In this paper, we designed and fabricated four different types of HTS-TFT based on double sided YBCO thin film and measured their respective operating parameters (including winding resistance, winding inductance, coupling coefficient, and qualityfactor) at liquid nitrogen temperature (LN 2 , 77 K). As the comparative experiment to the HTS-TFT, we also developed the same four types of copper (Cu)-TFT and measured their parameters at both room temperature (RT, 298 K) and LN 2 , to evaluate their behavior. It can be found from the comparative experiments between the HTS-TFTs and Cu-TFTs that the HTS-TFTs (in LN 2 ) possess better operating parameters than the Cu-TFTs (in LN 2 and RT) and they operate as expected in the power conversion tests. The significance of this work is that the HTS-TFTs can be employed in wireless power transfer systems and other power conversion fields, offering a performance enhancement to power transmission efficiency. Keywords: high temperature superconducting thin film transformer, power conversion, double sided YBa 2 Cu 3 O 7−x (YBCO) thin film