Abstract: A series of high-entropy ceramics with the nominal composition (Mg_0.5Zn_0.5)_0.4+xLi_0.4(Ca_0.5Sr_0.5)_0.4−xTiO₃ (0 ≤ x ≤ 0.4) has been successfully synthesized using the conventional solid-phase method. The (Mg_0.5Zn_0.5)_0.4+xLi_0.4(Ca_0.5Sr_0.5)_0.4−xTiO₃ ceramics are confirmed to be composed of the main phase (Zn,Mg,Li)TiO₃ and the secondary phase Ca_0.5Sr_0.5TiO₃ by X-ray diffractometer, Rietveld refinement, and X-ray spectroscopy analysis. The quality factor (Q×f) of the samples is inversely proportional to the content of the Ca_0.5Sr_0.5TiO₃ phase, and it is influenced by the density. The secondary phase and molecular polarizability (α_T) have a significant impact on the dielectric constant (ε_r) of the samples. Moreover, the temperature coefficient of resonant frequency (τ_f) of the samples is determined by the distortion of TiO₆ octahedra and the secondary phase. The results indicate that (Mg_0.5Zn_0.5)_0.4+xLi_0.4(Ca_0.5Sr_0.5)_0.4−xTiO₃ ceramics achieve ideal microwave dielectric properties (ε_r = 17.6, Q×f = 40900 GHz, τ_f = −8.6 ppm/°C) when x = 0.35. (Mg_0.5Zn_0.5)_0.4+xLi_0.4(Ca_0.5Sr_0.5)_0.4−xTiO₃ ceramics possess the potential for application in wireless communication, and a new approach has been provided to enhance the performance of microwave dielectric ceramics.