Low-temperature X-ray diffraction experiments revealed the existence of two low-temperature phases of Ag7NbS6, phase II (between about 280 and 140 K) and phase III (between about 140 and 10 K). The powder pattern of the phase II measured at 245 K could be indexed on the basis of monoclinic unit cell, A = 29.467(5), B = 14.770(3), C = 12.768(2) Angstrom, and beta = 124.28(1)degrees. A probable assignment on the basis of a monoclinic superstructure model is proposed for the powder pattern of the phase III measured at 100 K.