A water-soluble supramolecular-structured photoinitiator (SSPI) was synthesized by supramolecular self-assembling between methylated beta-cyclodextrin (M beta CD) and hydrophobic 2,2-dimethoxy-2-phenylacetophenone (DMPA). The structure of SSPI was characterized by X-ray diffraction, FTIR, H-1 NMR, UV-vis, and fluorescence spectra. The results indicated that M beta CD and DMPA had formed 1 : 1 inclusion complex in methanol solution. The binding constant (K) for the complex was 7.51 x 10(2)M(-1). SSPI could be dissolved in water easily and its water-solubility was 15.3 g/100 mL. SSPI was the more efficient photoinitiator than DMPA for the photopolymerization of acrylamide (AM) in homogeneous aqueous system. The conversion for photopolymerization of trimethylolpropane triacrylate system initiated by SSPI was similar to that initiated by DMPA. (c) 2007 Periodicals, Inc.