Abstract (Bi1.5Zn0.5−xMgx)(Zn0.5Nb1.5)O7 (x=0.0, 0.1, 0.2, 0.3, 0.4) dielectric ceramics with improved dielectric properties were prepared by a conventional mixed oxide route. The effects of Mg2+ ion substitution on the microstructures and dielectric properties based on structural characteristics in this system were investigated systematically. Rietveld refinement was used to analyze the structural change of the sintered samples. Microscopic analysis showed that all of the samples maintained the (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 phase. The shift of the peaks can be demonstrated by changing the unit cell volumes caused by the substitution of ions. The dielectric constant εr was related to the relative density. The bond valence of (Bi1.5Zn0.5−xMgx)(Zn0.5Nb1.5)O7 ceramics was calculated to evaluate the relationship between the temperature coefficient of the dielectric constant τε and the structural characteristics of the B site ion. The loss tangent tanδ was mainly affected by the densities and grain size. The (Bi1.5Zn0.5−xMgx)(Zn0.5Nb1.5)O7 ceramics with improved dielectric properties were obtained at a low sintering temperature of 950°C, which could be a promising candidate for low temperature co-fired ceramics (LTCC) and multilayer components applications in high frequency and microwave range.