An organic light-emitting device includes a first electrode, a second electrode disposed opposite to the first electrode, and an organic layer disposed between the first electrode and the second electrode and including an emission layer. The emission layer includes at least one first light-emitting material represented by Formula 1 and at least one second light-emitting material represented by Formula 2: and X1 to X12, Ar1, M, X21 to X24, A, B, R1 to R12, R21, R22, a1, a2, n, L, M in Formulae 1 and 2 are defined as in the specification.