Disclosed are an Indium Tin Oxide (ITO) film, wherein nitrogen-containing compounds produced by reactions of nitrogen with at least one atom selected from the group consisting of In, Sn and O atoms which are constitutional elements of ITO, or deposited nitrogen-containing compounds are present on a surface of the ITO film; and a method for preparing an ITO film, comprising the step of treating a surface of the ITO film with nitrogen plasma. An organic electroluminescent device using the ITO film provided by the present invention as an anode shows a low voltage, a high efficiency and a long lifetime.