In the present work, non-stoichiometric 0.9Mg2+xSiO4+x-0.1CaTiO3 ceramics with nero-zero if were prepared by using the conventional solid-phase reaction method. The effects of additional magnesium contents on the sintering behavior, phase evolution, microstructure, and microwave dielectric properties of the ceramics were investigated. Based on the XRD analysis, the relationship between phase composition and microwave dielectric properties was investigated. The if value was closely related to secondary phase, such as MgSiO3 and Mg2TiO4. The Q x f and er depended on the grain size distribution and porosity. Optimally, samples with a x value of 0.075 and sintering at 1425 degrees C for 3 h showed microwave dielectric characteristics of er = 9.78, high Q x f = 68,048 GHz and near-zero if = + 4.57 ppm/degrees C. As a result, the 0.9Mg2+xSiO4+x-0.1CaTiO3 ceramics are regarded a potential candidate for microwave dielectric applications.