High quality epitaxial YBa2Cu3O7−x(YBCO) thin films have been deposited onto ferrimagnetic yttrium iron garnet (100) substrates using a double buffer layer lattice engineering scheme. The YBCO films arec‐axis oriented and show superconductive transition temperatures of 88–89 K with transition widths ≤0.5 K. The films also exhibitedJc’s of 2.7×106A/cm2in zero field and 1.1 ×106A/cm2in 2000 G at 77 K. Dielectric resonator measurements indicated unloadedQvalues of 29 000 at 77 K and 24 GHz for unpatterned films. These values correspond to a surface resistance (RS) of 500 &mgr;&OHgr; at 77 K, 10 GHz, which is the lowest obtained to date for a YBCO film on a ferrimagnetic substrate. Such films could be used for fabricating miniature‐high‐temperature superconducting microwave elements such as nonreciprocal and passive microwave devices, making possible, their integration on a single ferrimagnetic wafer. ©1995 American Institute of Physics.