An organic light-emitting device including a substrate; a first electrode on the substrate; a second electrode; an organic layer between the first electrode and the second electrode, the organic layer including an emission layer; and a first layer including a cyano group-containing compound, the first layer being between the first electrode and the emission layer, wherein the first electrode includes an Al-based reflective layer and a transparent conductive layer sequentially stacked on the substrate, the Al-based reflective layer including a first element and nickel (Ni), and the first element includes at least one of lanthanum (La), cerium (Ce), praseodymium (Pr), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).