A SrRuO3 (SRO) buffer layer has been developed for growth of superconducting YBa2Cu3O7 (YBCO) thick films on polycrystalline metal substrates where a biaxially oriented MgO layer—produced by ion-beam-assisted deposition (IBAD)—was used as a template. By using such an architecture, we have routinely deposited YBCO films with an in-plane mosaic spread in the range of 3°–6° in full width at half maximum. A critical current density of 3.0×106 A/cm2 in self-field at 75 K for a film thickness of over 1.3 μm has been achieved. We believe that the SRO buffer layer plays a significant role in the much improved performance of YBCO conductors built on IBAD MgO. The features of SRO, such as good lattice match with both MgO and YBCO, excellent thermal stability in an oxidizing environment, and planarization of growing surface, make it the ideal choice as the buffer layer for high-performance superconductor coatings. © 2002 American Institute of Physics.