An organic light-emitting device includes: a first electrode; a second electrode facing the first electrode; m emission units stacked between the first electrode and the second electrode, each emission unit including at least one emission layer; and m−1 charge generating layers respectively located between two adjacent emission units among them emission units, each of the charge generating layers including one n-type charge generating region and one p-type charge generating region, wherein m is an integer of 2 or more, and at least one of the m−1 p-type charge generating regions includes a phosphate-containing compound.