A novel type of amphiphilic spherosilsesquioxane derivative,: 1-(1,omega-propylenemethoxy)oligo(ethylene oxide)-3,5,7,9,11,13,15-heptahydridopentacyclo [9.5.1(3,9).1(5,15).1(7,13)]octasiloxane has been prepared from (HSiO3/2)(8) and allyl-functional oligo(ethyleneoxide) (M-n=750 g/mol) by hydrosilylation. The monosubstituted octahydridosilsesquioxane was characterized by H-1, C-13 and Si-29 NMR spectroscopy, IR, and MALDI-TOF mass spectroscopy as well as elemental analysis. Surface: tension measurements of the water-soluble amphiphile show a cmc in the range of 6 x 10(-4) mol/L. Aggregation of the uncondensed amphiphile leads to micellar and vesicular structures that can be cross-linked to liposome-like silica particles at elevated pH.