Effect of host polymers on energy transfer in phosphorescent dye doped polymer light emitting devices has been investigated. Poly (N-vinylcarbazol) [PVK] and poly (9,9'-di-n-hexyl-2,7-fluorene-alt-1,4(2,5dinhexyloxy) phenylene) [PFHP] were examined as the host materials for the phosphorescent dyes fac tris(2-phenypyridine) irdium(III) [Ir(ppy)3] and 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) [PtOEP]. The host and guest materials have the large spectrum overlap between the emission of the hosts and absorption of the guests. When the guests were doped in PVK, the singlet-singlet and triplet-triplet energy transfer took place efficiently. On the contrary, the energy transfer did not take place from φ-conjugated polymer PFHP to the guests, even though common requirements for Förster and Dexter energy transfer were fulfilled. Host aggregation in PFHP based phosphorescent dye doped light emitting devices can play an undesired role obstructing efficient energy transfer.