We have synthesized 4-[(4-nitrophenyl)ethynyl]benzoic acid (NPBA) as a hole injection material for the modification of ITO surface and fabricated OLEDs consisting of ITO/NPBA self-assembled monolayer (SAM)/TPD (600 angstrom)/Alq3 (600 angstrom)/Al (600 angstrom). The effects of ITO modified with NPBA SAM exhibited lower driving voltage than the device using 4-nitrobenzoic acid (NBA). Also, we have examined the interface properties between the modified ITO and adjacent organic layer from the measurements of contact angle and atomic force microscopy (AFM).