Bi3.25La0.75Ti3-xNbxO12 (x=0-0.1) thin films were prepared by depositing sol-gel solutions on Pt/Ti/SiO2/Si < 100 > substrates. The remanent polarization increased by around 26% and the coercive field reduced by around 4% in the Nb-doped film with x = 0.04. The substitution tolerance of Nb5+ for Ti4+ was limited to x=0.04 due to the large difference of the ionic radius between Nb5+ and Ti4+ cations and the pyrochlore-phase Bi2Ti2O7 appeared after-wards, which was observed for the first time in doped Bi4Ti3O12 films. The leakage current density of the Nb5+-doped Bi3.25La0.75Ti3O12 (BLT) films was found to be lower than that in pure BLT films due to the appearance of highly insulating Bi2Ti2O7 phase for x > 0.04. The morphology of BLT films was modified by the Nb-doping. BLT and Nb-doped with x=0.04 film showed a decrease in polarizations of 22% and 16%, respectively, of their initial valve after 1010 switching cycles. The Nb-doping improved the fatigue endurance by 27% for the doping concentration where the remanent polarization was increased. (c) 2005 Elsevier B.V All rights reserved.