An organic light emitting device includes a substrate, a first electrode on the substrate, a second electrode, a first stack on the first electrode and including a hole injection layer, a first hole transport layer, a first mixed layer, a second hole transport layer, a first light emitting layer, and a first electron transport layer sequentially laminated, a second stack between the first stack and the second electrode and including a third hole transport layer, a fourth hole transport layer, a second light emitting layer, and a second electron transport layer sequentially laminated, and a charge generation layer between the first stack and the second stack to control charge balance between the first and second stacks. The first mixed layer includes materials used to form the first and second hole transport layers.