Na₂(Th_xU_1−x)(MoO₄)₃ and Na₄(Th_xU_1−x) (MoO₄)₄(x=0.5 and 0.8) were synthesized, by reacting (Th_xU_1−x)(MoO₄)₂ with Na₂MoO₄ in appropriate molar ratios at 873K in an evacuated quartz ampoule for 25h. While Na₂(U_0.5Pu_0.5)(MoO₄)₃ and Na₄(U_0.5Pu_0.5)(MoO₄)₄ were synthesized, by reacting (U_0.5Pu_0.5)(MoO₄)₂ with Na₂MoO₄ in appropriate molar ratios at 873K in argon atmosphere for 45h. The crystal structure of these compounds were derived from powder XRD data in atetragonal system (space group: I4₁/a) by Rietveld profile method. Thermogravimetric curves of Na₂(Th_xU_1−x)(MoO₄)₃ and Na₄(Th_xU_1−x)(MoO₄)₄ did not show any weight changes up to 973 K in helium atmosphere. High temperature X-ray diffraction (HTXRD) studies of Na₂(Th_xU_1−x)(MoO₄)₃ and Na4(Th_xU_1−x)(MoO₄)₄ in vacuum showed positive thermal expansion in the temperature range of 298 to 873K.