The performance of polymer light-emitting diodes was optimized by dispersing titania nanotubes into different functional layers. When titania nanotubes are doped into the hole-transport layer, the hole mobility of the device is greatly increased due to the good p-type conductibility of titania nanotubes. In the case of doping titania nanotubes into emitting layer, irradivative recombination was decreased since organic molecules wrapped on outer surface or entering into the nanotube make the chain conformation of polymer molecules more open. At last, the device efficiency of PLEDs was greatly improved by doping titania nanotubes into the hole buffer layer. This contributes to strong interaction between the titania nanotube and the polymer. This interaction reduces not only the hole conductibility but also the creation of defect states on interface region which can quench the luminescence.