A series of NaCu3Ti3SbO12 ceramics were prepared by the conventional solid-state reaction technique under different sintering temperature conditions. Their crystalline structure, microstructure, dielectric properties, and complex impedance were systematically investigated. It has been found that they are in general quite similar to CaCu3Ti4O12 ceramics reported in the literature, showing giant dielectric permittivity properties with epsilon' as high as 104. Within the measuring frequency range of 40-100 MHz, a single dielectric relaxation with the characteristic frequency around 1 MHz is seen at room temperature or below, whereas an additional one in the low-frequency region is also observed at high temperatures. Dielectric properties and microstructures change largely with sintering temperature, and a small amount of CuO secondary phase and Cu2+/Cu+, Ti4+/Ti3+ and Sb5+/Sb3+ aliovalences exist in these NaCu3Ti3SbO12 ceramics. On the basis of an electrode comparison experiment, the two dielectric relaxations are ascribed to an internal barrier layer capacitance effect and an electrode polarization effect, respectively.