Three Keggin-type polyoxometalates functionalized by amino acids, (C5H13N2O2)2(H3O)PMo12O40·8H2O 1, (C5H14N2O2)2SiMo12O40·12H2O 2 and (C5H14N2O2)2GeMo12O40·12H2O 3, were synthesized and characterized by elemental analysis, IR and 1H NMR spectra and single-crystal X-ray diffraction. The X-ray crystallographic study showed that the structures of the three compounds involved N-H···O and O-H···O hydrogen bonds among the protonated ornithine cations, water molecules and the heteropolyanion cluster, and thus represent a model interaction between polyoxometalates and proteins. These complexes display inhibitory actions to the human cancer cells Hela and PC-3 m in vitro.