An organic light emitting device with improved light emitting efficiency, the organic light emitting device includes a substrate, a first electrode arranged on the substrate, a second electrode arranged to face the first electrode, an organic light-emitting layer arranged between the first electrode and the second electrode, an electron transport layer arranged between the organic light-emitting layer and the second electrode, wherein the electron transport layer includes a multi-layer structure that includes at least one first layer and at least two second layers, wherein ones of said at least one first layer and ones of said at least two second layers are alternately stacked, wherein ones of the at least two second layers are arranged at both opposite ends of the electron transport layer, each of the at least two second layers having a lower electron mobility than that of each of the at least one first layer.