Three novel hybrid open-framework lanthanide sulfate–oxalates, {[NH 4 ][Ln(H 2 O)(SO 4 )(C 2 O 4 )]} n [Ln=Y (I), La (II), Sm (III)] have been synthesized via hydrothermal reaction, and characterized by single crystal X-ray diffraction, powder X-ray diffraction, infrared spectrophotometry, thermal gravimetric analysis and fluorescence analysis. These three compounds were isostructural, and all crystallized into the monoclinic system with space group of P2 1 /n. In their structures, LnO 8 dodecahedra, SO 4 tetrahedral and C 2 O 4 groups are linked to give rise to a three-dimensional open-framework, which contains two kinds of 12-membered ring channel systems running along the a and b axis, respectively.