The evolution of the physical properties and of the crystal structure of the Li 1−xNbO 2 system has been studied as the function of Li-stoichiometry. We showed that the induction of superconductivity by Li removal is accompanied by the appearance of a superstructure with doubled c axis. X-ray single crystal determination of this superstructure reveals that Nb cations of the different layers have different valences due to interlayer ordering of Li vacancies.