Congo red dye has been postgrafted onto mesoporous silica that was prepared by the controlled hydrolysis of tetraethyl orthosilicate in the presence of organic agents. Surface grafting of mesoporous silica having amino groups as initiator sites was prepared from gamma-aminopropyl-trimethoxysilane by sol-gel process. The postgraffing reaction of Congo red onto silica with terminal amino groups was achieved by a repeated step of the addition of methyl acrylate to amine groups followed by the amidation of the resulting ester moieties with ethylene diamine. Postgrafting efficiency of all materials has been outlined. Because postgrafting efficiency values have been found to be smaller than theoretical values, it is concluded that the resulting product was more likely to be a hyperbranched polymer rather than a true dendrimer at higher generations. The postgrafted structures with amino-terminal groups provide an attractive site for binding Congo red dye that not only persists in its characteristic properties, but also has exceptional hybrid properties possessed by mesoporous silica. (C) 2003 Wiley Periodicals, Inc.