The compounds in Na2O-MoO3 system were prepared by the solid-state reaction route. The phase composition, crystal structures, microstructures, and microwave dielectric properties of the compounds have been investigated. This series of compounds can be sintered well at ultra-low temperatures of 505 degrees C-660 degrees C. The sintered samples exhibit good microwave dielectric properties, with the relative permittivities (epsilon(r)) of 4.1-12.9, the Qxf values of 19900-62400GHz, and the (f) values of -115ppm/degrees C to -57ppm/degrees C. Among the eight compounds in this binary system, three kinds of single-phase ceramics, namely Na2MoO4, Na2Mo2O7 and Na6Mo11O36 were formed. Furthermore, the relationship between the structure and the microwave dielectric properties in this system has been discussed. The average Na-I-O and Mo-VI-O bond valences have an influence on the sintering temperatures in Na2O-MoO3 system. The large valence deviations of Na and Mo lead to a large temperature coefficient of resonant frequency. The X-ray diffraction and backscattered electron image results show that Na2MoO4 doesn't react with Ag and Al at 660 degrees C. Also, Na2Mo2O7 has a chemical compatibility with Al at 575 degrees C.