Thin films of Y1Ba2Cu3Oxhave been produced on sapphire substrates by d.c. diode sputtering in Ar atmosphere followed by annealing O2at 850 C. X‐ray diffraction and resistivity show the films are amorphous and insulating as sputtered but become polycrystalline and conductive upon annealing, whereupon resistance begins to fall at 98 K, becoming fully superconductive at 69 K with a mid‐point at 86 K. Four‐point resistance measurements are made using low frequency phase sensitive detection. Electron microprobe analysis indicates that the 1‐2‐3 composition of this oxide can be obtained in the film by using a Y1Ba3.2Cu3.9Oxtarget, suggesting that resputtering of Ba and Cu occurs during the deposition. A strong interaction (most likely diffusive) can occur with the sapphire substrate which degrades the superconducting transition, necessitating shorter annealing times and lower temperatures than used for bulk powders.