Low-temperature X-ray diffraction studies revealed the existence of two low-temperature phases of an argyrodite-family compound Ag7TaS6 that contains mobile Ag ions at room temperature, the phase II (between about 280 and 170 K) and the phase III (between about 170 and 10 K). The powder pattern of the phase II could be indexed on the basis of an orthorhombic unit cell, A = 7.442, B = 7.403 and C = 10.531 Angstrom. A probable assignment on the basis of tetragonal superstructure model was proposed for the powder pattern of the phase III.