Highly efficient electrophosphorescence from light-emitting devices based on two types of rhenium(I) diimine complexes, (1,10-phenanthroline)Re(CO)3Cl (phen-Re) and (2,9-dimethyl-1,10-phenanthroline)Re(CO)3Cl (dmphen-Re), is reported. N, N′-di-1-naphthyl-N, N′-diphenylbenzidine is used as the hole-transporting layer. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline is used to confine excitons within the luminescence zone. phen-Re and dmphen-Re are doped into the host material (4,4′-N-N′-dicarbazole)biphenyl with mass ratios of 2–20% as the light-emitting layer, respectively. The maximum efficiency and brightness achieved from the devices based on phen-Re and dmphen-Re are 6.67 cd/A and 2769 cd/m2, and 7.15 cd/A and 3686 cd/m2, respectively. © 2004 American Institute of Physics.