By　means　of　high　resolution　transmission　electron　microscopy　(HREM)　and　high-angle　annular　dark-field　image　technique　(HAADF),　morphological,　structural　and　compositional　characteristics　of　the　precipitates　in　the　Mg-4Y-3Nd　alloy　aged　at　200°C　for　different　periods　of　time　have　been　studied.　On　the　basis　of　HREM　observations,　an　atomic　structural　model　for　the　β＇-precipitate　with　an　orthorhombic　unit　cell　has　been　proposed.　The　characteristic　distribution　of　the　precipitates　which　are　rich　in　rare-earth　elements　(Y,　Nd)　has　been　clearly　revealed　by　the　HAADF　imaging　technique.