We demonstrate very high efficiency electro phosphorescence in organic light-emitting diodes (OLEDs) employing a phosphorescent molecule doped into a conductive host material. Electrophosphorescent OLEDs were fabricated with bis(2-(2'benzo[ 4,5-a]thienyl)pyridinato-N,C-3') iridium(acetylacetonate) [btp(2)Ir(acac)] as a pure red phosphor which has photoluminescence spectrum centered at 615 nm. The device structure was as follows; ITO/2-TNATA/NPB/btp(2)Ir(acac) doped in host/BCP/Alq(3)/Liq/Al. CBP, BCP and Alq(3) were used as a host, and the concentration of btp(2)Ir(acac) was varied from 8 to 11%. The device with 11% btp(2)Ir(acac) doped in Alq(3) showed saturated electroluminescence (EL) peak at 615 nm and an efficiency of 4.76 cd/A with an initial brightness of 1100 cd/m(2). The CIE coordinates of the device showed x = 0.67, y = 0.32 at a current density of 1mA/cm(2). The photoluminescence spectrum of Alq(3) centered at 510nm is sufficiently overlap with absorption of dopant, therefore, energy transfer from host to guest is efficient.