Abstract: The different solution of rare earth modifier (La, Ce, Pr, Nd and Sm) were used to modify glass fiber (GF) and silica (SiO₂), the glass fiber-SiO₂/polytetrafluoroethylene (GF-SiO₂/PTFE) composites of 55wt% SiO₂ and 2wt% GF were mixed by a high-speed dispersion machine and prepared by hot-pressing. The effects of rare earth modifier on the properties of the composites material were investigated, such as the water absorption, the thermal, the dielectric properties, the tensile strength and morphology. The FTIR method was used to investigate the structures of rare earth La, unmodified filler and modified filler. The surface morphology and element were analyzed by SEM and EDS. The results show that rare earth La is superior to other rare earth modifier in promoting the interfacial adhesion between glass fiber and polytetrafluoroethylene (PTFE) and improving the water absorption, the coefficient of thermal expansion, the dielectric properties and tensile properties of the GF-SiO₂/PTFE composites due to the stable electronic structure of rare earth La and the strong attraction to the anion.. The dielectric properties of the GF-SiO₂/PTFE composites is mainly affected by the content of rare earth La, and the optimum performance of the GF-SiO₂/PTFE composites is obtained at 0.3wt% rare earth La content.