Fused silica was prepared by different approaches, and the microwave dielectric properties were investigated. For the fused silica sintered at 1100°C by solid-state sintering, the dielectric constant (εr) and Qf value increased with increasing the sintering time up to 5 h, while the temperature coefficient of resonant frequency (τf) decreased. The optimal properties with low εr of 3.72, high Qf value of 44,300 GHz, and low τf of −14.4 ppm/°C were achieved when sintered at 1100°C for 5 h. The microwave dielectric properties could be further improved by other preparing approaches, as listed below: εr = 3.90, Qf = 63,500 GHz, τf = −5.7 ppm/°C for spark plasma sintering, and εr = 3.83, Qf = 122,100 GHz, τf = −8.3 ppm/°C for melting method. The results showed that fused silica was a good candidate as a microwave substrate material.