Electrophosphorescence has been observed in phosphorescent blend polythiophene LEDs with poly(3-methyl-4-octyl-thiophene) (PMOT) as host, bis (2-phenylbenzothiazole) iridium acetylacetonate (BTIr) as the guest. Investigation of photoluminescence and quantum yields shows that energy transfer exists in the host-guest system and depends on guest concentration. Electroluminescence indicates that charge trapping effect also contributes to the formation of exciton at phosphorescent centers.