An　oxalate-assisted　lanthanide　(Ln)　incorporation　strategy　is　first　demonstrated　for　creating　rare　high-nuclearity　Ln-containing　polyoxoniobates　(PONbs).　With　the　strategy,　a　series　of　high-nuclearity　Ln-containing　PONbs　of　50-nuclearity　Dy2Nb48,　103-nuclearity　Dy7Nb96,　200-nuclearity　Dy10Nb190,　and　206-nuclearity　Dy14Nb192have　been　made,　showing　an　increasingly　large　structure　evolution　from　Dy2Nb48monomer　to　Dy7Nb96dimer　and　to　distinct　Dy10Nb190and　Dy14Nb192tetramers.　Among　them,　Dy14Nb192presents　the　largest　heterometallic　PONb　and　also　the　PONb　with　the　greatest　number　of　Ln　ions　reported　thus　far.　Interestingly,　both　giant　Dy14Nb192and　Dy10Nb190molecules　can　further　undergo　single-crystal　to　single-crystal　intermolecular　aggregations,　forming　infinite　{Dy14Nb192}∞and　{Dy10Nb190}∞chains,　respectively.　The　former　structural　transformation　shows　a　reversible　humidity-dependent　aggregation-disaggregation　process　accompanied　by　a　proton　conductivity　response,　while　the　latter　structural　transformation　is　irreversible.　These　new　species　largely　enrich　the　very　limited　members　of　Ln-containing　PONb　family　and　offer　rare　examples　for　studying　structural　transformations　between　giant　molecular　aggregates　and　infinitely　extended　structures　at　the　atomic　level.　©　2022　American　Chemical　Society.　All　rights　reserved.