Here, we report highly efficient blue organic light-emitting diodes (OLEDs) with Mes2 B [p-4, 4' -biphenyl-NPh(1-naphthyl)] (BNPB) as a blue emitter. It is found that both efficiencies and electroluminescent color are very sensitive to the selection of electron transport materials in the devices. For an optimized structure [indium tin oxide/2,3,5,6-tetrafluoro-7,7,8,8- tetracyanoquinodimethane (1 nm) N, N' -di(naphthalen-1-yl)- N, N' -diphenyl-benzidine (45 nm) /BNPB (20 nm) /1,3,5-tris(2- N - phenylbenzimidazolyl) benzene (30 nm) /LiF (1 nm) /Al] with BNPB as an undoped blue emitter, a maximum current efficiency can reach 3.5 cdA. It is found that BNPB emits two distinct peaks, one of around 450 nm and the other of 485 nm, and their respective emission intensities depend on the nature of majority charge carrier in the emission layer. © 2008 American Institute of Physics.