Disclosed is a method of forming an ITO film by optimized sequential sputter deposition of seed and bulk layers having different sputter process conditions, which is applicable to various display devices, and more particularly, to an organic light-emitting device needing an ultra-planarized surface roughness. In forming a transparent conducting electrode of a display device on a transparent substrate with an ITO film including a seed layer and a bulk layer, a method of forming the ITO film includes a first sputter deposition step of forming the ITO film on the substrate with sputtering gas supplied to an ion source at an ambience of oxygen flowing in the vicinity of the substrate and a second sputter deposition step of forming the ITO film with the sputtering gas supplied to the ion source only, wherein the first and second sputter deposition steps have different process conditions, respectively and wherein the seed and bulk layers are deposited by the first or second sputter deposition step.