Degradation of piezoelectric properties has been studied in ferroelectric PZT films by means of optical interferometry. The degradation under de bias and aging of poled films have been observed. The decay of piezoelectric coefficient with time is described by a logarithmic law with aging rates comparable to those of switching polarization. The aging rates are shown to be sensitive to poling conditions and to orientation of the poling field with respect to the direction of preferred polarization. The fatigue measurements revealed a decrease of piezoelectric coefficient with a simultaneous shift of piezoelectric hysteresis loops. Degradation tests on thin membranes covered by PZT films have been reported.