Abstract: Indium-tin oxide （ITO） surfaces are treated by sonication cleaning, O<SUB<2</SUB< plasma and UV-ozone. The treated surfaces are then observed with an atomic force microscopy （AFM）. The organic light emitting devices （OLEDs） with the same structure of glass/ITO/NPB/Alq<SUB<3</SUB</Al but different ITO surface treatments are prepared to study the influence of treatment of ITO surfaces on the performance of OLED. The results show that the chemical composition and configuration of ITO surface have been changed by these treatments. And the luminance, lifetime and stability of the device can be improved dramatically by the treatment, especially by that of O<SUB<2</SUB< plasma.