We report the structural and longitudinal piezoelectric responses (d33) of epitaxial Pb(Zr0.52Ti0.48)O3 (PZT) films on (001) SrTiO3 and Si substrates in the thickness range of 40 nm–4 μm. With increasing film thickness the tetragonality of PZT was reduced. The increase in d33 value with increasing film thicknesses was attributed to the reduction of substrate constraints and softening of PZT due to reduced tetragonality. The d33 values of PZT films on Si substrates (∼330 pm/V) are higher than those on SrTiO3 substrates (∼200 pm/V). The epitaxial PZT films on silicon will lead to the fabrication of high performance piezoelectric microelectromechanical devices.