The crystal structure and the properties of a new microwave dielectric ceramics x SrTiO3–(1 − x)Sr(Mg1/3Nb2/3)O3 have been investigated. With x = 0.025, The new microwave dielectric ceramic achieves the dielectric properties of a dielectric constant ɛr ∼27.8, a Q × f value ∼26,800, and a τf value ∼7.4 ppm/°C. When the SrWO4 is added, the sintering temperature of x SrTiO3–(1 − x)Sr(Mg1/3Nb2/3)O3 ceramics will fall to 1350 °C, and its Q × f value can be improved further and the τf value becomes smaller. When the SrWO4 is added by 0.07 mol, the specimen acquires the following microwave properties: a dielectric constant ɛr ∼30.3, a Q × f value ∼29,500, and a τf value of approximately −0.4 ppm/°C.