We investigated the effects of the ultrathin film of a new cathode underlayer material, lithium tert-butyl cyclopentadienide (Li-TBCPD), on the electron injection efficiency and performance of the Alq3-based OLED. The current density-voltage-luminance (I-V-L) and the luminous efficiency characteristics of the [ITO/alpha-NPB (40 nm)/Alq3 (60 nm)/Li-TBCPD (1.0 nm)/Al] device were examined. The device with the Li-TBCPD/Al bilayer cathode demonstrated the current density of 360A/m(2) at 12V and the maximum luminance of 8,100 cd/m(2), while the device with the LiF/Al cathode showed 70A/m(2) and 5,800 cd/m(2), respectively. This improvement seems to originate from the relatively lower bond dissociation energy of Li-TBCPD and hence the easiness of lithium layer formation beneath the aluminum cathode.