Composite ceramics based on the spinel Mg2TiO4 were prepared by a conventional mixed-oxide route. To achieve the temperature stabilization of the dielectric constant, each of the composites was added with 7 mol% CaTiO3. The effect of the substitution of isovalent Co for Mg on the microstructure and the microwave dielectric properties of the composite ceramics was also investigated. A maximum Q x f value of around 150-160 THz was obtained for the undoped Mg2TiO4, whereas a reduced Q x f value was observed for an increase in the Co concentration in the system (1-x)Mg2TiO4-xCo(2)TiO(4). Upon doping with 7 mol% CaTiO3, the Q x f value passed through a maximum with increasing Co concentration. Adding ZnO-B2O3 to the composite system based on Co-doped Mg2TiO4 resulted in a reduction of the sintering temperature by 150 degrees-200 degrees C without any significant degradation in the Q x f value.