Niobium-doped (Pb0.8Ba0.2)ZrO3 (PBNZ) thin films were prepared by RF-magnetron sputtering at room temperature followed by postannealing at 700 °C. The doping concentration of Nb is in the range from 0 up to 2.5 at%. The introduction of Nb enhances the ferroelectric property and suppresses the leakage current of the PBNZ films. A large remanent polarization (Pr) of 2Pr=35 μC/cm2 can be obtained from a doping of 1.5 at% Nb in the PBNZ film in comparison to that of 19 μC/cm2 from the undoped PBZ film. The Pt/PBNZ/Pt capacitor also exhibits a high fatigue resistance against polarization switching up to 1010 cycle as that of Pt/PBZ/Pt. Moreover, an improvement of retention property can be also achieved from Nb doping.