A series of NaCu 3 Ti 3 Sb 0.5 Ta 0.5 O 12 ceramics were prepared by conventional solid-state reaction technique at different sintering temperatures. Their crystalline structures, microstructures, dielectric properties and complex impedance were systematically investigated. All the ceramics show the main phase of perovskite-related crystallographic structure, and their dielectric properties change significantly with sintering temperature. Those ceramics sintered above 1020°C perform high dielectric-permittivity properties with ε' over 3000. Impedance spectroscopy analysis reveals that NaCu 3 Ti 3 Sb 0.5 Ta 0.5 O 12 ceramics are electrically heterogeneous and composed of semiconducting grains and insulating grain boundaries. Moreover, a small amount of CuO secondary phase and Cu 2+ /Cu + , Ti 4+ /Ti 3+ , Sb 5+ /Sb 3+ and Ta 5+ /Ta 3+ aliovalences are found to exist in NaCu 3 Ti 3 Sb 0.5 Ta 0.5 O 12 ceramics through XRD and XPS analysis. Internal barrier layer capacitance effect suggests the origin of the high dielectric-permittivity properties in NaCu 3 Ti 3 Sb 0.5 Ta 0.5 O 12 ceramics.