Effects of lanthanum (La) substitution (0.003 <= x <= 0.015) on the dielectric and ferroelectric properties of Pb(Zr0.5Ti0.5)O-3 thin films have been investigated. The films were synthesized on the Pt(111)/Ti/SiO2/Si (100) substrates by a sol-gel method. Large dielectric constants of the films are obtained within range of 800-1600 which are almost comparable to those observed in bulk ceramics. The films also show improved remnant polarization values and reduced coercive field values with the increasing addition of La substitution. Our results suggest that low La substitution contributes to enhance film electric properties due to the improvement of non-180 degrees domain wall mobility as well as the stabilization of tetragonal phase. (C) 2010 Elsevier B. V. All rights reserved.