Provided is an organic light-emitting device including a first electrode, a second electrode disposed opposite to the first electrode, an emission layer disposed between the first electrode and the second electrode, and an electron-transporting layer disposed between the emission layer and the second electrode. The electron-transporting layer includes a first electron-transporting material and a second electron-transporting material. The lowest unoccupied molecular orbital (LUMO) energy level of the first electron-transporting material (EL1) and the lowest unoccupied molecular orbital (LUMO) energy level of the second electron-transporting material (EL2) satisfy the equation 0.1 eV≦|EL1−EL2|≦0.3 eV.