Due to their hi-h dielectric constant and low losses properties, BaxSr1-xTiO3 (BSTO) compounds are interesting candidates as capacitor dielectrics. The similarity of their lattice parameters with the YBa2Cu3O7-delta (YBCO) high-T-c superconductor, allows high quality multilayers growth and offers the possibility to combine low microwave losses in superconding electrodes with electric control of the dielectric constant, to realize electrically tunable low loss microwave devices. In this paper, we present a study of in situ fabrication of superconducting YBCO/ferroelectric BSTO bilayers and YBCO/BSTO/YBCO trilayers on MgO substrates using pulsed laser deposition (PLD). Growth mechanisms and microstructures are investigated by MET, SEM and RHEED analyses. AC and DC electrical characterizations are done to study the conduction mechanisms. The aim of these studies is to control m situ epitaxial growth of the bilayers (300 nm for YBCO and from 300 to 900 nm for BSTO) in order to develop low temperature superconducting YBCO/ferroelectric BSTO/superconducting trilayers capacitors, the capacitance of which can be tuned via an applied DC electric field. Parallel plate capacitors are prepared by consecutive in situ deposition of the constituent layers. A tunable YBCO/BSTO(x=0.67)/YBCO capacitor have been realized with good electrical characteristic at 77 K. (C) 2003 Elsevier B.V All rights reserved.