Red electrophosphorescence from light-emitting devices based on two rhenium(I) diimine complexes, (4,4′-dimethyl formate-2,2′-bipyridine)Re(CO)3Cl (dmfbpy-Re) and (4,4′-dibutyl formate-2,2′-bipyridine)Re(CO)3Cl (dbufbpy-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, bathocuproine is used to confine excitons within the luminescence zone. dmfbpy-Re and dbufbpy-Re are doped into the host materials (4,4′-N-N′-dicarbazole)biphenyl with mass ratios of 2%–20% as the light-emitting layer. Red emission from both complexes is achieved and the main peaks of both photoluminescence and electroluminescence are at about 610 nm. The turn-on voltage, maximum efficiency, and brightness for red emission achieved from the devices based on dmfbpy-Re and dbufbpy-Re are ∼ 5 V, 1.3 cd/A, and 582 cd/m2 and ∼ 4 V, 1.1 cd/A, and 739 cd/m2, respectively. © 2003 American Institute of Physics.