A series of new microwave dielectric ceramics with ultralow dielectric loss in Na2O-WO3 binary system were prepared by the modified solid-state reaction method at ultra-low sintering temperatures. Three stable phases, namely Na2WO4, Na2W2O7 and Na2W4O13, were formed in the system. Their stability in the air, phase composition, compatibility with metal electrodes, microstructures, and microwave dielectric properties were investigated. In this binary system, the cubic structure Na2WO4 ceramic sintered at 565 degrees C exhibited the best microwave dielectric properties with a permittivity of 5.6, a Q x f value of 124200GHz and a temperature coefficient of -63ppm/degrees C at a frequency of 13.1GHz. The Na2WO4 ceramic is chemically compatible with Ag and Al electrodes. Besides, the Na2WO4 ceramic has favorable stability in the air. Due to the excellent dielectric properties and favorable stability in the air, the Na2WO4 ceramic is a great candidate for LTCC devices.