A new molybdenum(VI) complex, K 2 (NH 4 ) 6 [Mo 8 O 24 (C 2 O 4 ) 4 ], was prepared and characterized by chemical analysis, and IR spectral and X-ray studies. Thermal decomposition studies were made using TG, DTA and DTG techniques. The compound is anhydrous and decomposes between 538 and 633 K in two steps. The first step extends up to 603 K to give an intermediate compound with the tentative composition K 2 (NH 4 2 ) 2 [Mo 8 O 24 (C 2 O 4 ) 2 ], which decomposes in the second step to give a mixture of potassium tetramolybdate (K 2 Mo 4 O 13 ) and molybdenum trioxide (MoO 3 ) at 633 K. DTA also shows a peak at 800 K which corresponds to the melting of potassium tetramolybdate. An examination of the products obtained at 633 and 803 K using chemical analysis, IR spectra and X-ray studies reveals that they are identical.