The oxygen partial pressure (pO2) dependent conductivity of Nd3+ doped PZT was investigated at different temperatures in order to get information on the nature of the conducting charge carriers and on the chemical oxygen diffusion coefficient. From a positive slope close to 0.25 in log (conductivity) vs. log (pO2) plots it is concluded that PZT with donor-type Nd3+ shows predominant hole conduction already at moderately high oxygen partial pressures, while under reducing conditions electron conduction prevails. This unexpected occurrence of hole conduction in a nominally donor doped system is interpreted in terms of the only partially controllable loss of lead oxide during preparation, which results in the formation of lead vacancies. Those act as acceptors at the temperatures employed in this study (560–615 °C) and turn the nominally donor doped material into a slightly acceptor doped one. From the conductivity relaxation after partial pressure changes, chemical oxygen diffusion coefficients could be extracted and values of about 6.5·10−9 cm2/s at 560 °C and 2·10−8 cm2/s at 611 °C are found in air.