It is an object of the present invention to provide a method for manufacturing a highly reliable display device with a preferable yield. A method for manufacturing a display device according to the invention comprises the steps of: forming a first electrode including a conductive material added with a material which prevents crystallization; forming a layer containing an organic compound over the first electrode by heating the first electrode under a reduced pressure at temperatures of 350° C. or higher; and forming a second electrode over the layer containing an organic compound. It is preferable to perform the heat treatment at temperatures of 350° C. or higher, preferably, 375° C. or higher for 12 hours or longer. When the first electrode is formed by using indium tin oxide containing silicon oxide, a highly display device can be manufactured.