Li_2x(Zn_0.95Co_0.05)_2−xSiO₄ (0 ≤ x ≤ 1) ceramics were prepared through the conventional solid-state route. A fixed amount of Li₂O–MgO–ZnO–B₂O₃–SiO₂ (LMZBS) glass was used as a sintering aid to help lower the sintering temperature to around 900 °C. The effects of part lithium-ion substitution on the phase formation, sintering behaviour, microstructures and microwave dielectric properties of the ceramics were systematically investigated. When x = 0.25, the sample achieved a dense microstructure and exhibited excellent microwave dielectric properties of ε_r = 6.47, Q × f = 131 579 GHz and τ_f = −27.12 ppm °C⁻¹. For its practical application in low-temperature co-fired ceramics (LTCC), large positive τ_f of CaTiO₃ was used to adjust the τ_f value of the composite ceramic to nearly zero. The composite ceramic of 0.975Li_0.5(Zn_0.95Co_0.05)_1.75SiO₄–0.025CaTiO₃ sintered at 900 °C also presented good microwave dielectric properties of ε_r = 6.773, Q × f = 69 177 GHz and τ_f = −2.45 ppm °C⁻¹.