An all chemical route has been used to produce substrates-nanostructured by self-assembled oxide nanoislands-and to grow YBa2 Cu3 O7-x (YBCO) films on top. A great increase in the superconducting properties has been observed at high temperatures and magnetic fields parallel to the YBa2 Cu3 O7-x c -axis. The vortex pinning properties and the defects induced in the YBa2 Cu3 O7-x matrix have been investigated. We show that extended defects along the c -axis, induced in the YBCO matrix by the interfacial nanostructures, lay at the origin of the improved performances. © 2009 American Institute of Physics.