- In course of a study of high strength, ductile alloys based on the Mg–Li system, we have identified a new quaternary phase with a composition of Mg 31 Zn 26 Ca 13 Li 8. The structure of this phase was investigated by Transmission Electron Microscopy (TEM) using the Convergent Beam Electron Diffraction (CBED) technique. Full atomic model is proposed using direct methods applied to powder X-ray diffraction data. The phase has a cubic primitive unit cell with lattice parameter a= 9.386 (8) Å and its crystal symmetry belongs to the P m 3¯(No. 200) space group. The unit cell of the new phase exhibits a new structure type, which is a variant of the Mg 2 Zn 11 structure. The reliability factors characterizing the Rietveld refinement procedure are: R p= 8.6%, R wp= 12.4%, RB= 6.9% and R f= 4.4%.