A simple route to synthesize polyhedral silsesquioxanes, (RSiO1.5)n, by the hydrolytic condensation of modified aminosilanes, is reported. The starting material was N-(beta-aminoethyl)-gamma- aminopropyltrimethoxysilane, a trifunctional aminosilane. It was reacted with a stoichiometric amount of phenylglycidyl ether in sealed ampules at 50 °C for 24 h, leading to the trisubstituted product plus a series of oligomers arising from the intermolecular reaction between methoxysilane groups and the secondary hydroxyls generated by the epoxy-amine reaction. When this product was subjected to hydrolytic condensation using a variety of catalysts (HCl, NaOH, HCOOH) and a thermal cycle attaining 150 °C, polyhedral silsesquioxanes (SSQO) were obtained. Their molar mass was independent of reaction conditions as revealed by size exclusion chromatography. Characterization by 1H, 13C, and 29Si NMR suggested that the main product was a mixture of polyhedral SSQO with n ) 8 and 10; i.e., T8 and T10. Due to the high OH functionality, i.e., 24 OH groups in T8 and 30 OH groups in T10 polyhedra, the synthesized product may be used as a cross-linking unit of very high functionality or as a modifier for several polymeric materials.