The behavior of grain and grain-boundary conductivity of acceptor (Sc)-doped (Ba,Ca)(Ti,Zr)O-3 ceramics sintered in moist reducing atmosphere and subsequently reoxidized in dry and moist atmosphere was investigated by means of impedance spectroscopy (IS). In moist firing atmosphere, water vapor was found to react with oxygen vacancies, forming positively charged hydroxyl defects (OH)0. on regular oxygen sites in the crystal lattice. Proton hopping is considered to raise the ionic conductivity significantly. Therefore, hydroxyl defects (OH)0. in turn influence the grain conduction. Hydroxyl defects (OH)0. are also considered to be responsible for alternations of the dielectric maximum at the Curie point.