(Ba_1−xSr_x)₄(Sm_0.4Nd_0.6)_28/3Ti₁₈O₅₄ (x = 0.02, 0.04, 0.06, 0.08, 0.1) solid solutions were prepared by the conventional solid-state reaction process. It was found that (Ba_1−xSr_x)₄(Sm_0.4Nd_0.6)_28/3 Ti₁₈O₅₄ ceramics are fully composed of BaSm₂Ti₄O₁₂ and BaNd₂Ti₅O₁₄ phases for all the compositions. The increasing x value (0.02 ≤ x ≤ 0.1) in (Ba_1−xSr_x)₄(Sm_0.4Nd_0.6)_28/3Ti₁₈O₅₄ ceramics can not only obtain high Q × f value but also effectively enhance the permittivity ( ${\epsilon }_{\text{r}}$). The (Ba_1−xSr_x)₄(Sm_0.4Nd_0.6)_28/3Ti₁₈O₅₄ ceramic with x = 0.08, sintered at 1440 ℃ for 4 h, shows excellent microwave dielectric properties of permittivity ( ${\epsilon }_{\text{r}}$) ≈ 93.19, quality factor (Q × f) ≈ 9770.14 GHz (at 3.415 GHz), and almost near-zero temperature coefficient of resonant frequency ( ${\tau }_f$) ≈ +4.56 ppm/℃.