Abstract Samples of Fe( Ta x Nb 1− x ) 2 O 6, with 0 ≤ x ≤ 1, were synthesized and studied by x-ray diffraction and Mössbauer spectroscopy. The sample with x = 0 is orthorhombic, while those with x ≥ 0.55 are tetragonal. The samples with 0.001 ≤ x ≤ 0.50 are not single-phase. So, under the present experimental conditions, the orthorhombic series of the title system is highly unstable, while the tetragonal series can dissolve up to about 45 at. % Nb.