In this study, 0.94Mg(1‐3x/2)CexTiO3−0.06(Ca0.8Sr0.2)TiO3 (MCexT−CST, 0≤x≤0.01) composite ceramics were prepared at a low temperature of 1175°C by using the 50‐nm‐sized powders. The effects of Ce3+ doping on crystalline phase, microstructure, and microwave dielectric properties of MCexT−CST were studied. A main ilmenite (Mg,Ce)TiO3 phase and a minor perovskite (Ca0.8Sr0.2)TiO3 phase coexist well with the appearance of impurity MgTi2O5 phase in MCexT−CST. The dielectric properties of MCexT−CST are affected by the molecular polarizability, the impurity phase, and the Ce3+ doping. The replacement of Mg2+ by high valence Ce3+ could effectively inhibit the formation of oxygen vacancy, resulting in the enhancement of Q×f. When x = 0.005, MCexT−CST exhibits microwave dielectric properties with a moderate εr of 21.5, a high Q×f of 67 000 GHz, and a near‐zero τf of −0.74 ppm/°C. The results reveal that the Ce3+ substitution is a prospective approach to optimize the microwave dielectric properties of MgTiO3‐based ceramics.