High purity (Tl0.5Pb0.5)(Ba0.2Sr0.8)2Ca2Cu3Ox superconducting 20–60 µm thick films with Tc (0)-values of between 110 and 115 K and transition widths of 2–4 K were fabricated on polycrystalline9 mol% Y2O3 doped ZrO2 (YSZ) substrates by screen-printing. The microstructure and the phase composition at theinterface of the superconducting Tl-1223 film and the substrate were analysed usingtransmission electron microscopy, scanning electron microscopy, selected area electrondiffraction and energy dispersive x-ray fluorescence analysis. The interface between thesubstrate and the superconducting film consisted of several phases formed by the reactionbetween the thallium superconductor and zirconium dioxide. Analyses of the substrate/filminterface performed using energy dispersive x-ray fluorescence showed the presence of aBa–(Pb–Sr)–Zr–O compound close to the substrate. This phase was responsible for thevery good adhesion of the superconducting films to the YSZ substrates. The additionalphases found at the interface were CaO, calcium strontium cuprates and bariumcuprate.