Abstract: Organic light-emitting diodes（OLEDs） using TiO₂ ultra-thin films as a hole injecting buffer layer of different thicknesses were prepared by RF magnetron sputtering. The diodes with a typical structure of ITO/TiO₂/TPD/Alq₃/Al（TPD : N,N’-diphenyl-N,N’-bis（3-methylphenyl）-1,1’-diphenyl-4,4’-diamine, Alq₃: tris（8-quinolinolato）-aluminum） show better electroluminescent properties in comparison with the samples without TiO₂ buffer layer. The investigation on the effects of the thickness for TiO₂ shows that EL efficiency of the device, which contains 1 nm TiO₂ buffer layer, is improved to 2 cd/A by approximately 100% in comparison with the device without buffer layer at the current density of 100mA/cm². It can be attributed to the limit of the injecting number of hole and the improvement of the balance of hole and electron injections by the TiO₂ ultra-thin film with suitable thickness as a hole buffer layer.