The efficiency of the organic light-emitting devices (OLEDs) with a 2,9-dimethyl-4,7-diphenylphenanthroline (BCP) hole blocking layer (HBL) between a N, N'-bis-(1-naphthyl)-N, N'-diphenyl-1, 1'-biphenyl-4,4'-diamine (NPB) hole transport layer (HTL) and a tris-(8-hydroxyquinoline) aluminum (Alq3) emitting layer (EML) was higher than that of the OLEDs without a HBL. The dominant electroluminescence (EL) peak corresponding to the Alq3 layer for the OLEDs with a BCP HBL between a NPB HTL and an Alq3 EML appeared at the almost same position as the EL peak for the OLEDs without a HBL. The Commission Internationale de l'Eclairage chromaticity coordinates of the OLEDs corresponded to a stabilized green color, regardless of the existence of the BCP HBL layer.