Low-temperature X-ray diffraction measurements on a correlated-electron superconductor Mo3Sb7 revealed that the high-temperature cubic state with the Ir3Ge7 type structure (space group Im (3) over barm) transforms to tetragonal below Ts = 53 K, at which spin-gap formation was recently Suggested. The effect of electron correlations to the Structural instability is briefly discussed in connection with the condensation of the high-temperature local moments to the spin-singlet-like state. (C) 2008 Elsevier Ltd. All rights reserved.