The effect of Zr content on the crystal structure and electrical properties of barium zirconate titanate (Ba(Zr,Ti)O3) was studied by X-ray diffraction and dielectric, ferroelectric and impedance spectroscopy. An increase of Zr content into BaTiO3 leads to a reduction in its c-parameter and an increase in its a-parameter, resulting in a change from tetragonal to cubic symmetry of the BaTiO3 unit cell. The Curie temperatures are lowered and the relative permittivity values are decreased with increasing Zr content. The presence of BaZrO3 secondary phases has the affect of decreasing tanδ. A higher applied electric field is required during the polarization process because of the effect of domain-wall pinning caused by oxygen vacancies. Impedance spectroscopy studies of Ba(Ti 0.95Zr0.05)O3 ceramics show a decrease in the bulk resistance with increasing temperature, indicating a typical negative temperature coefficient of resistance. © 2007 Springer-Verlag.