Polycrystalline ZnO films were fabricated using rf magnetron sputtering under different oxygen flow rates (P O ). The surface morphology of the films can be affected by changing P O , and the average surface roughness decreases with the increasing P O . The increasing P O can improve the grain growth with (002) orientation. Typical ZnO infrared vibration bands have been observed at 408 and 513cm −1 , and the full width at half maximum of the infrared peak decreases with the increase of P O due to the improved crystallinity. The optical band gap (E g ) of the polycrystalline ZnO films increases from 3.22eV at P O =0sccm to 3.25eV at P O =10sccm because the defects decrease with the increasing P O . The photoluminescence peaks in the region of 2.4–2.7eV are from the transition between conduction band edge and oxide antisite defects (O Zn ), and also be influenced by oxygen vacancies (V O ).