Donor-doped PbZr0.52Ti0.48O3 (PZT) films were utilized to study the effect of dopants on the mobility of ferroelectric domain walls. For chemical solution deposited PZT films 2 mu m in thickness, doped with 1%- 4% Nb or La, the low field dielectric permittivity remained between 1100 and 1300. With increasing Nb concentration, both the reversible and irreversible Rayleigh constants increased from epsilon(init) and alpha' of 1150 and 39 cm/kV, respectively, for undoped PZT films to 1360 and 43 cm/kV for films doped with 2 mol% Nb. La doping increased the irreversible Rayleigh constant but did not strongly affect the reversible Rayleigh parameter. These observations are consistent with softening of the dielectric and electromechanical response with donor doping.