Abstract: A series of genistein’s phosphates were synthesized through a simplified Atherton-Todd reaction and the structures of the phosphates were determined by electrospray ionization mass spectrometry (ESI-MS) and NMR. In case of monophosporyl derivatives, NMR spectra show that substitutions occur at the 7-position of genistein but not at its 4′ and 5-position. Moreover, the non-covalent complexes of lysozyme with the four new genistein phosphates were detected by ESI-MS.