Grain growth as a function of annealing temperature in Y–Ba–Cu oxide superconducting thin films is presented. Effects of excess Cu on the temperature dependence of the resistance, grain growth, and sheet resistivity are discussed. This is the first systematic study of the microstructure of thin films formed by the nonvacuum technique of metallo organic deposition. The Cu-rich films show an anomalous behavior in the resistivity at 220–240 K. The presence of excess Cu was found to enhance grain growth for films annealed below the melting point of the 1–2–3 phase. Films deposited on 〈100〉 SrTiO3 and rapid thermal annealed showed partial epitaxial growth of the 1–2–3 phase. The analytical techniques of Rutherford backscattering spectrometry, ion channeling, x-ray diffraction, scanning electron microscopy, electron microprobe analysis, sheet resistivity, and temperature versus resistance measurements have been used in this study.