An OLED and a flat panel display, the OLED including an anode; a cathode; and an organic, the organic layer including an EML, the EML including first and second hosts, a hole transport region between the anode and the EML and including at least one of a hole injection layer (HIL), a hole transport layer (HTL), a buffer layer, or an electron blocking layer (EBL), an electron transport region between the EML and the cathode, the electron transport region including at least one of a hole blocking layer (HBL), an electron transport layer (ETL), or an electron injection layer (EIL), and an intermediate layer between the EML and the electron transport region; wherein an electron affinity of a compound of the intermediate layer [EAintermediate layer] and an electron affinity of the first host [EAhost1] satisfy a relationship represented by the following expression: EAintermediate layer≧EAhost1+0.3 eV.