In this work, the polytetrafluoroethylene (PTFE)-based composite substrates were manufactured by mixing, calendering, hot-pressing sintering. The composition of all the samples was PTFE, SiO2 and chopped E-glass fibers. The effects of content of E-glass fibers on the properties of the SiO2 filled PTFE composites were investigated, including density, water absorption, dielectric properties (εr, tanδ), coefficient of thermal expansion (CTE) and temperature coefficient of dielectric constant (τε). The compositions of inorganic materials mixture are (62 ? x) % SiO2 + x % E-glass fiber (x: mass ratio to composites, x = 0, 1, 1.5, 2, 2.5, 3). The results show that as the content of E-glass fibers is 2.5 wt.%, this composite obtains optimal properties, including excellent dielectric properties (εr~2.9123, tanδ~0.0011), acceptable water absorption of 0.075%, temperature coefficient of dielectric constant of 10 ppm/?C and coefficient of thermal expansion of 15.87 ppm/?C.