In this paper, some electrostrictive constants of the polarized and non-polarized lead zirconate titanate (PZT) ceramics are measured. To measure electrostrictive constants, a new dynamic measurement method for the capacitance variation with step and alternating stress is developed. This new method enables us to obtain the electrostrictive constants in the state of fixed polarization without an aging effect. Using the measured value of the electrostrictive constant 2d3333 of nonpolarized PZT ceramics and the remanent polarization P3 of the fully polarized one, the piezoelectric strain constant d33 is calculated. This calculated result agrees with the measured one very well.