The CaTiO3 doping Mg2B2O5 microwave dielectric ceramics were synthesized by the traditional solidstate reaction method. The effects of CaTiO3 doping on the microwave dielectric properties and micro structure of the samples were studied using XRD, SEM and microwave dielectric properties measurements. The results show that the Mg2B2O5 and CaTiO3 phases can coexist, and the dielectric constant and the temperature coefficient of resonant increase with the increase of the content of CaTiO3 while the quality factor slightly decreases. When the mass fraction of Mg2B2O5 is 5% , the CaTiO3 ceramics sample sintered at 1 085 ℃ for 4 h shows optimal properties, that is,εr=7.03,Q×f=42 221 GHz,τf= -2.8×10-6 ℃-1.