The heteropolytungstate [As4W40O140Ce(H2O)5]Na25· 63H2O is prepared by the reaction of NaWO4·2H2O with NaAsO2 and Ce(NO3)3·6H2O. Its structure is determined by X-ray diffraction and element analysis. The cell parameters of [As4W40O140Ce(H2O)5]Na25·63H2O are as follows:a=3.1252(8)nm, b=2.2656(6)nm, c=1.3973(9)nm, α=β=γ90°,V=9. 893(7)nm^3 , space group P21/m21/m2/n.In the anion [As4W40O140Ce(H2O)5 ]^25-, the ring-type ligand (As4W40O140)^28- consists of four bridging WO6 octahedras that connect four B-α-(AsW9O33)^9- subunits yb sharing two cis oxygen atoms with each one. The four B-α-(AsW9O33) ^9- subunits in the anion do not lie in the same plane but in a up- down-up arrangement. The center ion Ce^3+ does not completely fit into the cavity of eigher S1 or S2. There are nine oxygen atoms coordinating to Ce(Ⅲ), with four oxygen atoms coming from four extra WO6 octahedras respectively and five oxygen atoms from five water molecules. The anion has a C2v symmetry.

Key words: HETEROPOLYACID, TUNGSTATE, ARSENIC COMPOUNDS, CERIUM COMPOUNDS, X-RAY DIFFRACTION ANALYSIS, ELEMENTAL ANALYSIS