The influence of ultraviolet (UV) illumination on piezoelectric properties is investigated in lead zirconate titanate (PZT) thin films. It is found that the poling procedure is more effective when the film is exposed to a broadband UV light in the presence of a high electric field. Piezoelectric coefficients are increased and aging rates are decreased as compared to poling in dark conditions. Both an internal bias field and a polarization offset are observed in the piezoelectric hysteresis loops. The mechanism of the photoinduced poling effect in PZT films is probably due to electron trapping near the film-electrode interface. (C) 1997 American Institute of Physics. [S0003-6951(97)00541-X].