We have measured the work function for various indium-tin oxide (ITO) substrates using cyclic voltammetric method, where the cyclic voltammetric system was constructed using a three-electrode compartment electrochemical cell consisted of a ITO and Al as the working electrode, a platinum wire as the counter electrode, and Ag/Ag+ (0.1 M AgNO3) as the reference electrode. And we have investigated the relation ship between the work function and the power efficiency of the OELD having a structure of glass substrate/ITO/TPD/BeBq(2)/Li:Al. The work functions of the ITO substrates with a sheet resistance of 7, 10, 15, and 30 ohm/cm(2) were 4.70, 4.78, 4.81, and 4.77 eV, respectively. It was also found that the ionization potential (IP) and electron affinity (EA) of BeBq(2) were 5.5 eV, and 2.9 eV, respectively.