Li6Zr2O7 crystallizes in a framework structure with Li occupying 1D channels in three distinguishable square–pyramidal sites. Rao et al. have reported a factor 100 increase in Li+ conductivity at 300°C by substitution of Ta(V) for Zr(IV). We demonstrate here that a similar enhancement in Li-ion conductivity can also be achieved by incorporation of interstitial Li in the formula unit Li6+x Zr2−x M x O7 (M=Y or In). Insertion of x =0.15 Li in the form of Li6+x Zr2−x M x O7 can be obtained by simple solid state synthesis. In order to know the limit of Li insertion into Li6Zr2O7, we demonstrated electrochemical insertion into Li6+x Zr1.5Ti0.5O7 of excess Li to at least x ≈0.17 at room temperature. The Lithium activation energy was 0.63eV for Li6.15Zr1.85Y0.15O7.