The crystal structures and the microwave dielectric properties of (1-x)CaTiO 3 -xCa(Mg 1 / 3 Nb 2 / 3 )O 3 perovskite ceramic system have been investigated. (1-x)CaTiO 3 -xCa(Mg 1 / 3 Nb 2 / 3 )O 3 solid solution exhibited orthorhombic crystal structures for all compositions. With x = 0.66, a new microwave dielectric ceramic material 0.34CaTiO 3 -0.66Ca(Mg 1 / 3 Nb 2 / 3 )O 3 applicable to microwave devices is suggested and possesses the dielectric properties of a dielectric constant r ~ 48, a Qxf values ~ 32,500 (at 6.7 GHz) and a τ f value ~-2 ppm/ o C at 1450 o C for 3 h. Further improvement of the Qxf value can be achieved by extending the sintering time to 6 h. It reveals a higher Qxf value of 34,000 (at 6.7 GHz) without degrading other microwave dielectric properties of 0.34CaTiO 3 -0.66Ca(Mg 1 / 3 Nb 2 / 3 )O 3 ceramics.