A　rare　sandwich-type　heteropolyoxoniobate　cluster,　[Eu(H2O)3Te6Nb18O64(OH)4]15−　{EuTe6Nb18},　has　been　isolated　by　simultaneously　incorporating　a　lanthanide　cation　and　tellurite　anions　into　polyoxoniobate.　The　{EuTe6Nb18}　cluster　represents　the　first　example　of　lanthanide-incorporated　telluroniobate　with　unprecedented　Eu-Te　heterometal　cations　in　the　sandwiched　sites.　The　N-HO　hydrogen　bonds　link　the　copper-amine　complexes　and　{EuTe6Nb18}　polyoxoanions　into　a　3D　supramolecular　framework　1　with　pcu　topology.　Furthermore,　compound　1　exhibits　moderate　proton　conduction　and　water　vapor　adsorption　properties.　©　2022　The　Royal　Society　of　Chemistry