Layered double hydrotalcites pillared by heteropolyoxometalates, ZnAl-SiW11 and ZnAl-SiW(11)Z (Z = Co2+, Ni2+ and CU2(+)) have been synthesized by an anion-exchange reaction. The powder X-ray diffraction spectra and IR analysis show that the compounds are layered complexes with gallery heights of 0.99 nm and the anions entering the layer retain their Keggin structure. The decomposition temperatures of these complexes in air decrease in the following order : ZnAl-SiW,,Ni (620 K), ZnAl-SiW11Co (614 K), ZnAl-SiW11Cu (608 K), ZnAl-SiW11 (602 K), ZnAl-NO3 (563 K). The XRD patterns of the compounds treated in boiling solutions with different pH for 2 h reveal that the layer framework is stable in the pH range from 3.6 to 7.5. The synthesized materials, especially ZnAl-SiW11Co, show high catalytic activities for the oxidation of benzaldehyde to benzoic acid using H2O2 in a liquid-solid biphase system.