An amphiphilic dithiafulvene oligomer was synthesized by cycloaddition polymerization of aldothioketene generated from 1,4-diethynylbenzene and a PEO-grafted phenylacetylene (feed ratio 5/1). The degree of polymerization was determined as 6 by H-1 NMR analysis. The aggregation behavior of the oligomer was studied in the mixed solvent of D2O and DMSO-d(6). Effective charge-transfer interaction of the oligomer and hydrophilic methyl viologen was observed in an aqueous solution. (c) 2007 Wiley Periodicals, Inc.