Multicomponent excited-state emissions from monomer, exciplex and electroplex were observed in a bilayer organic electroluminescent device with a structure of ITO/TPD(60nm)/PBD(60nm)/Al(where TPD and PBD stand for N,N′diphenylN,N′bis(3-methylphenyl)1,1′biphenyl4,4′diamine) and (2(4′biphenyl)5(4″tertbutylphenyl)1,3,4oxadiazole, respectively). The difference between the photoluminescence of this device and the TPD∶PBD equimolar evaporated films suggests that the exciplex takes place only at the interface of TPD/PBD. The Variation of electroluminescence spectra with bias indicates the different formation mechanisms and the different population of each excited state component, as well as the different dynamic recombination process of carriers in this device.