In this paper, the microwave dielectric characteristics and microstructures of (1_x)(Mg1_y,Zny)TiO3–xCaTiO3 (x =0.07¨0.11,y =0.2¨0.4) ceramic system were studied. The replacement of Mg2+ ion with Zn2+ ion increases the dielectric constant and quality factor.The phase composition of the system changes from Mg2TiO4 to MgTiO3 during the sintering, which improves the dielectric properties.CaTiO3 increases the dielectric constant, reduce the loss and also compensate the temperature coefficient of (Mg,Zn)TiO3. The existing areaof the different compositions in the ceramics was observed by means of energy dispersive spectroscopy, which reveals that CaTiO3 coexistswith (Mg,Zn)TiO3 in minor crystal grain. And the existing of CaTiO3 phase can inhibit abnormal grain growth of the phase of (Mg,Zn)TiO3.A dielectric constant er of 22.5, a Q_f value of 86,000 (at 7.5 GHz) and a sf value of +3 ppm/-C were obtained for 0.91(Mg0.7,Zn0.3)TiO3–0.09CaTiO3 ceramics sintered at 1310 -C for 3 h.