We investigated effects of oxygen deficiency in the indium tin oxide (ITO) on the performance of poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV)-based polymer light-emitting diodes, in which the ITO anode was deposited by radio frequency magnetron sputtering at different oxygen flow rates. We found that the degree of oxygen deficiency in the ITO films can affect the device performance significantly and is a source of current leakage. At the optimal oxygen flow rate, the leakage current of devices can be reduced and the balance between hole and electron fluxes can be promoted in the MEH-PPV layer to improve device efficiency. (C) 2008 Elsevier B.V. All rights reserved.