An organic electroluminescent display device and a method of preparing the same are provided. The organic electroluminescent display device may include a first electrode formed on a substrate. A second electrode may be formed so as to be insulated from the first electrode. One or more organic layers may be interposed between the first electrode and the second electrode and include at least an emission layer. A protective layer may be formed so as to cover the second electrode. The protective layer may have a surface roughness (rms) of about 5 Å to about 50 Å. The organic electroluminescent display device including a protective layer having a low surface roughness may benefit from superior lifespan characteristics.