Zn0.97Cu0.03O films were prepared by pulsed-laser deposition on c-cut sapphire substrates under various conditions in order to investigate the growth-dependent properties of the films. All the films exhibit room temperature ferromagnetism. Samples deposited at low temperature and low pressure show large saturation magnetization Ms. Moreover, the enhancement of Ms was observed in films annealed both in vacuum and in Zn vapor. However, postannealing in air led to the remarkable reduction of ferromagnetism. The results show that the itinerant electrons introduced by oxygen-deficient or Zn-rich atmospheres may play a significant role in room temperature ferromagnetism observed in this ZnCuO dilute magnetic semiconductor. It is consistent with carrier-induced ferromagnetism. The magnetization strongly depends on the appearance of free carriers and is relatively insensitive to whether they arose from VO or/and Zni.