Two new compounds, Rb3Na(MoO4)2 and Rb3Na(WO4)2, have been synthesized by conventional solid-state reaction. Single-crystal X-ray diffraction analysis revealed that they crystallize in the same space group P3¯m1 (No. 164) with the trigonal unit cell sizes of a = 6.138(2) A˚, c = 7.844(3) A˚ for the Mo compound and a = 6.161(4) A˚, c = 7.847(6) A˚ for the W compound. Both structures contain an infinite three-dimensional (3D) matrix that is built from isolated MO4 (M = Mo, W) tetrahedra, Rb(1)O 12, Rb(2)O10 polyhedra and NaO6 octahedra. In addition, the infrared spectroscopy spectrum (IR) and bond valence sums (BVS) calculations are used to verify the validity of the structures. The differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) results prove that both of them are congruently melting compounds. And the first-principle theoretical studies are also carried out to aid the understanding of their electronic structures.