Crack free Pb(ZrxTi1-x)O-3 (x = 0.45) films with various thicknesses were prepared by a sol-gel multiple coating process on Pt-coated Si(100) substrates. Rapid thermal annealing (RTA) methods were used to crystallize the amorphous PZT films. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) techniques were utilized to study the thickness dependent morphology and phase content. The relationship between the thickness and electrical properties of PZT films was investigated. The dielectric constants of PZT films increased with increasing film thickness. It was observed that the PZT films revealed spontaneous piezoelectric responses without poling process, which decreased with increasing film thickness. By poling the film with 26 V/mum, the piezoelectric responses of the thin PZT films was not obviously improved. However, the piezoelectric constant of thick PZT films increased obviously after poling. The phenomenon of thickness-dependent spontaneous polarization of PZT films was utilized to interpret the thickness dependent piezoelectric properties. The I-V characteristics and the dielectric breakdown strength of PZT films have also been examined and discussed.