A　novel　Fe-enriched　lamella　sandwich　phase　(χ-phase)　has　been　found　to　precipitate　along　the　basal　(0001)Mg　planes　in　the　heat-treated　Mg-Gd-Fe　alloy　and　its　structure　is　clearly　revealed　by　means　of　atomic-resolution　transmission　electron　microscopy.　The　layered　χ-phase　only　has　a　thickness　of　mono-unit-cell　and　consists　invariably　of　ten　atomic　layers　stacking　along　the　[0001]Mg　direction,　of　which　the　outermost　atomic　layers　had　larger　in-plane　atom-pillar　spacing　than　the　inner　layers.　Fe/Gd　atoms　are　mainly　enriched　in　the　outer　four　atomic　layers　in　the　χ-phase,　forming　two　structurally　unsymmetrical　four-layer　shells　to　sandwich　the　middle　two　Mg　layers.　An　atomic　model　has　been　proposed　for　this　layered　sandwich-structured　χ-phase.　©　2021,　Wuhan　University　of　Technology　and　Springer-Verlag　GmbH　Germany,　Part　of　Springer　Nature.