Relationships between the work function of indium tin oxide (ITO) and device performances of C60 modified organic light-emitting diodes were investigated. The work function of ITO was controlled by changing the degree of oxidation of ITO using ultraviolet/O-3 treatment. High efficiency could be obtained in the C60 modified device with short ITO treatment time, while driving voltage was lowered in the C60 modified device with long ITO treatment time. (C) 2007 Elsevier B.V. All rights reserved.