In this paper, the microwave dielectric characteristics and microstructures of (1−x)(Mg 1 − y ,Zn y )TiO 3 –xCaTiO 3 (x=0.07∼0.11, y=0.2∼0.4) ceramic system were studied. The replacement of Mg 2+ ion with Zn 2+ ion increases the dielectric constant and quality factor. The phase composition of the system changes from Mg 2 TiO 4 to MgTiO 3 during the sintering, which improves the dielectric properties. CaTiO 3 increases the dielectric constant, reduce the loss and also compensate the temperature coefficient of (Mg,Zn)TiO 3 . The existing area of the different compositions in the ceramics was observed by means of energy dispersive spectroscopy, which reveals that CaTiO 3 coexists with (Mg,Zn)TiO 3 in minor crystal grain. And the existing of CaTiO 3 phase can inhibit abnormal grain growth of the phase of (Mg,Zn)TiO 3 . A dielectric constant ɛ r of 22.5, a Q×f value of 86,000 (at 7.5 GHz) and a τ f value of +3 ppm/°C were obtained for 0.91(Mg 0.7 ,Zn 0.3 )TiO 3 –0.09CaTiO 3 ceramics sintered at 1310 °C for 3 h.