The　integration　of　lanthanide　(Ln)　ions　and　polyoxoniobates　(PONbs)　is　challenging,　and　the　known　Ln-substituted　PONbs　are　still　scarce.　This　work　introduces　high-nuclear　iso-Ln-oxo　clusters　into　the　PONb　system.　The　first　series　of　high-nuclear　Ln-oxo　clusters　encapsulated　heterometallic　polyoxoniobates　H9[Na(H2O)4][Cu(en)2]10{Ln6(μ3-OH)6(SiNb18O54)3}∙18H2O　(1-Ln,　en　=　ethylenediamine,　Ln　=　Dy,　Gd,　Tb,　Ho,　Er,　Tm,　Yb,　Lu)　based　on　flower-like　{Ln6(µ3-OH)6(SiNb18O54)3}　({Ln6Si3Nb54})　clusters　have　been　successfully　synthesized　via　one-pot　hydrothermal　synthesis　strategy.　The　flower-like　polyoxoanion　{Ln6Si3Nb54}　is　consisted　of　three　heteropolyoxoniobate　{SiNb18O54}　clusters　and　one　unique　planar　equilateral　triangle-shaped　{Ln6(μ3-OH)6}　cluster,　which　presents　the　highest　nuclear　iso-Ln-oxo　cluster　in　PONb　chemistry.　In　{Ln6(μ3-OH)6}　cluster,　each　pair　of　μ3-OH　groups　link　three　Dy3+　ions　to　form　a　small　approximate　equilateral　triangle-shaped　{Dy3(OH)2}　cluster.　Furthermore,　the　three　{Dy3(OH)2}　clusters　comprise　a　bigger　approximate　equilateral　triangle-shaped　{Dy6(μ3-OH)6}　cluster.　The　reported　hexanuclear　{Ln6}　cluster　skeletons　are　mostly　octahedral,　however,　such　equilateral　triangle-shaped　skeleton　of　the　hexanuclear　Ln-oxo　cluster　is　first　observed.　The　1-Dy　exhibits　good　water　vapor　adsorption　capacity　and　ferromagnetic　properties.　©　2023