Low-firing (Zn 0.9 Mg 0.1 ) 1−x Co x TiO 3 (x = 0.02–0.10) (ZMC x T) microwave dielectric ceramics with high temperature stability were synthesized via conventional solid-state reaction. The influences of Co 2 O 3 substitution on the phase composition, microstructure and microwave dielectric properties of ZMC x T ceramics were discussed. Rietveld refinement results show the coexistence of ZnTiO 3 and ZnB 2 O 4 phases at x = 0.02–0.10. (Zn 0.9 Mg 0.1 ) 1−x Co x TiO 3 ceramic with x = 0.06 (ZMC 0.06 T) obtains the best combination microwave dielectric properties of: ε r = 21.58, Q × f = 53,948 GHz, τ f = − 54.38 ppm/°C. For expanding its application in LTCC field, 3 wt% ZnO-B 2 O 3 -SiO 2 (ZBS) and 9 wt% TiO 2 was added into ZMC 0.06 T ceramic, great microwave dielectric properties were achieved at 900 °C for 4 h: ε r = 26.03, Q × f = 34,830 GHz, τ f = − 4 ppm/°C, making the composite ceramic a promising candidate for LTCC industry. [ABSTRACT FROM AUTHOR]