ZnO thin films were grown at various ambient pressures by pulsed laser deposition. After depositions, ZnO thin films were annealed at I atm of O-2 and forming gas (N-2:H-2=95:5), respectively. ZnO thin films were post-annealed in forming gas to investigate the relationship between the oxygen vacancies and the photoluminescence (PL), since hydrogen gas could desorb the oxygen from the surface and the grain boundary of the film. From the X-ray diffraction (XRD) pattern exhibiting only the (0 0 2) XRD peak of ZnO, all films were found to be c-axis-oriented. The results of PL spectroscopy and Hall measurement could suggest that the origin of the green luminescence of ZnO thin film comes mainly from the defect centers caused by the oxygen vacancies. (C) 2003 Elsevier B.V. All rights reserved.