A self-assembled monolayer (SAM) of 2,9,16-tri(tert-butyl)-23-(10-mercaptodecyloxy) phthalocyanine (HS-Pc) on the surface of a Au thin film has been employed as an anode in organic light-emitting diodes (OLEDs). Compared with the device without SAM, the turn-on voltage for the device with SAM decreased from 13 to 8 V and the external quantum efficiency (ηext) increased ca. 27 times as a result of the improvement of hole injection ability of the SAM. In addition, the device with Au−SAM as an anode showed higher efficiency (ηext = 0.66) than that of an indium tin oxide (ITO) glass anode (ηext = 0.33), which is commonly used in OLEDs.