This　study　reported　a　series　of　cube-shaped　polyoxoniobates,　{MCu12O8)(Cu12XmOn)(Nb-7(OH)O-21)(8)}　[M　=　Nb(1,　2),　Ln(3+)(3),　X　=　I(1,　m　=　3,　n　=　3;　2,　m　=　5,　n　=　1),　Br(3,　m　=　5,　n　=　1)].　As　the　first　octahedral　Cu12XmOn　cluster　incorporated　polyoxoniobate,　the　cube-shaped　three-shell　structure　of　{MCu12O8)(Cu12XmOn)(Nb-7(OH)O-21)(8)}　polyanion　contains　a　{MCu12O8}　body-centered　cuboctahedron,　a　{Cu12XmOn}　octahedron　and　a　{Cu-12(Nb-7(OH)O-21)(8)}　cube.　Compounds　1,　2,　3　show　effective　catalytic　activities　for　the　hydrolytic　decomposition　of　chemical　warefare　agent　simulants.