A poly(m-phenylene) derivative tethering carbazole unit (PmPCz) is reported to have a triplet energy level (E-T) as high as 2.64 eV, sufficient to host blue electrophosphorescence. To our best knowledge, this is the first conjugated polymer with E-T higher than that of state-of-the-art blue phosphorescent dopant, iridium(III) bis(4,6-(difluorophenyl)pyridinato-N,C-2)picolinate (FIrpic). PmPCz exhibits good thermal stability and excellent miscibility with the blue phosphorescent dopant, FIrpic. Owing to the high E-T and good miscibility, blends of PmPCz with FIrpic show no triplet energy back-transfer and exhibit emission exclusively from FIrpic, even at FIrpic concentration as low as 1 wt %. Single-layer blue phosphorescent polymer light-emitting diode based on the blend exhibits a luminance efficiency of 4.69 cd/A.