A novel two-dimensional solid, [{Cu(en)2}4(H4w12O42)]·9H2O (en =ethylenediamine), has been prepared under mild hydrothermal conditions.Single crystal X-ray diffraction revealed that each paradodecatungstate [H4W12O42]8-cluster in the title compound is connected with its four adjacent clusters through eight {Cu(en)2}2+bridging groups into a two-dimensional layered structure.Its cyclic voltammetric behavior in aqueous electrolyte demonstrated that its modified carbon paste electrode has a good stability.A probe reaction indicated that the catalytic activity of paradodecatungstates in epoxidation of maleic anhydride has been enhanced by assembling paradodecatungstate clusters into extended structures.