Using the Eu salt Langmuir-Blodgett (LB) film of a biphenylpyrazine derivative (C4BPy), we fabricated a double-heterostructure device with molecular-size emissive layer, ITO/diamine hole-transporting layer/Eu salt LB film of C4BPy (two monolayers)/oxadiazole electron-transporting layer/MgAg. When the DH device was driven at 170 K, only sharp red emission due to the Eu salt bimolecular layer was observed, and no emission due to the HTL and the ETL was observed. The result demonstrates that the C4BPy Eu salt bimolecular layer was successfully actuated as molecular-size emissive layer. The external quantum efficiency and maximum luminance of the device were 0.01% and 3 cd/m(2). respectively.