(1– x)CoTiNb 2O 8– xZnNb 2O 6 microwave dielectric ceramics were prepared via the conventional solid-state reaction route with the aim of reducing the τ f value and improving the thermal stability. The phase composition and the microstructure were investigated using X-ray diffraction, Raman spectra, and scanning electron microscopy. A set of phase transitions which were induced by composition had been confirmed via the sequence: rutile structure→coexistence of rutile and columbite phase→columbite phase. For (1– x)CoTiNb 2O 8– xZnNb 2O 6 microwave dielectric ceramics, the addition of ZnNb 2O 6 content ( x = 0–1) led to the decrease of ε r from 62.98 to 23.94. As a result of the high Q × f of ZnNb 2O 6 ceramics, the increase of ZnNb 2O 6 content also led to the lower sintering temperatures and the higher Q × f values. The τ f value was reduced from +108.04 ( x = 0) to − 49.31 ppm/°C ( x = 1). Among them, high density 0.5CoTiNb 2O 8–0.5ZnNb 2O 6 ceramics were obtained at 1175 °C with excellent microwave dielectric properties of ε r 39.2, Q × f 40013 GHz, and τ f + 3.57 ppm/°C.