Sol–gel-derived lead–zirconate–titanate (PZT) films doped with various amounts of niobium (Nb) have been spin coated on silicone substrates, and their remanent polarization Pr, and effective longitudinal and transverse piezoelectric coefficients (d33,c and e31,c) as well as the pyroelectric coefficient p, have been measured. The Zr/Ti ratio of the films is 53/47. Our results reveal that the Nb-dopant effects on the PZT films are very similar to the experimentally known effects on the corresponding bulk ceramics, i.e., enhancing both the longitudinal and transverse piezoelectric properties. However, because of the substrate clamping effect, the exact enhancement in the longitudinal piezoelectric properties cannot be evaluated by the d33,c measurement on the film samples. Accordingly, the observed d33,c value of the Nb-doped PZT films remains almost unchanged while the observed -e31,c (as well as Pr and p) increases with increasing Nb concentration, showing an optimum Nb concentration of 2 mol %. For the PZT film doped with 2% Nb, the observed values of Pr, d33,c, -e31,c, and p are about 30 μC/cm2, 95 pm/V, 18 C/m2, and 350 μC/m2 K, respectively. © 2004 American Institute of Physics.