Effects of sintering temperatures on the phases, microstructures, defect structures and dielectric behaviors of the SrTi0.985(Nb2/3Zn1/3)(0.015)O-3 ceramics have been systematically investigated. Giant permittivity (similar to 10100) and low tangent loss (similar to 0.035) are achieved in the ceramics sintered at 1500 degrees C. With an increase in sintering temperature, the grain size increases first and then stabilizes gradually, while the lattice constant increases first and then decreases. Higher sintering temperature is beneficial to the thermal stabilities of permittivity and tangent loss. Further investigations reveal that the giant permittivity mainly results from defect polarization. More Ti3+ ions and more oxygen vacancy-related defect complexes (Ti3+-VO-Ti3+ and VO-ZnTi '', etc.) are involved in the ceramics sintered at 1500 degrees C, contributing to the giant permittivity and low tangent loss. The presence of point defects breaks the local structural symmetry and distorts the oxygen octahedron. Dielectric properties are deteriorated at excessive sintering temperature due to the dissociation of defect complexes as well as the enhanced interfacial polarization.