We developed high-performance SiO2-based low-εr microwave dielec. composites via adding Sr3(PO4)2 and investigated their phase assemblages, sintering behaviors, microwave dielec. properties, thermal expansion coefficients (CTE), and mech. strengths in this paper.Adding Sr3(PO4)2 into SiO2 could successfully suppress the occurrence of microcracks in SiO2, tune the values of both temperature coefficient of resonant frequency (τf) and CTE, and enhance the flexural strength of the composite simultaneously.The composite with 22.5 % volume fraction (Vf) of Sr3(PO4)2 exhibits excellent combined properties with a low-εr (∼5.35), high Qxf value ( ∼73,717 GHz), near-zero τf value(∼ -1.1 ppm/°C), suitable high CTE value (∼17 ppm/°C), and acceptable high flexural strength (∼85Mpa) after sintering at the temperature of 1150°C/3 h.