The influence of the plasma treatment of the ITO (Indium Tin Oxide)/glass substrate was investigated in the fabrication of green OLEDs (Organic Light Emitting Devices) using the Alq(3)-C545T fluorescent system. Various plasma powers of 100 W, 150 W, and 200 W were used under the fixed conditions of an Ar/O-2 gas mixing ratio of 0.5 and pressure of 1m Torr during the plasma treatment. The threshold times required for the inter-insulator width between the subpixel regions to be reduced to 80% of their original value were found to be 4, 3, and 2 minutes at plasma powers of 100 W, 150 W, and 200 W, respectively. The plasma treatment durations at each power were varied from 1 minute up to the threshold time with intervals of one minute. The basic structure of the fabricated devices was 2TNATA/NPB/Alq(3)-C545T/Alq(3)/LiF/Al and the best emission characteristics were obtained in the case of the plasma treatment at 150 W for 2 minutes. The luminance and power efficiency of the device treated with the optimum plasma condition were 20000 cd/m(2) and 16 lm/W at 10V, respectively. The peak wavelength and the CIE coordinates were found to be 522nm and (0.32, 0.63), respectively.