An organic light-emitting device includes a first electrode; a second electrode; and an organic layer between the first electrode and the first electrode and including an emission layer (EML); a hole transport region between including an electron blocking layer (EBL) and at least one selected from a hole injection layer (HIL), a hole transport layer (HTL), and a buffer layer; and an electron transport region and including a hole blocking layer (HBL) and at least one selected from an electron transport layer and electron injection layer (EIL). A triplet energy of a material for the electron blocking layer (EBL T1), a triplet energy of a material for the hole blocking layer (HBL T1), and a triplet energy of a host in the emission layer (Host T1) satisfy Equation (1) and Equation (2): EBL T1≥HBL T1≥Host T1  (1) EBL T1−HBL T1≥0.2 eV  (2).