A novel oligoaniline with hierarchical flower-on-leaf microstructures has been fabricated via the oxidation of aniline in EtOH/water (3 : 7, v/v) mixtures. The as-prepared oligoaniline was characterized using the UV-vis, FTIR, 1 H NMR and MALDI-TOF MS techniques for analyzing the chemical structures.A possible formation mechanism has been proposed to interpret the growth of such hierarchical microstructures, and several inter-molecular interactions were suggested to drive the supermolecular assembly. The effect of the ethanol content in the medium on the morphology of the product was discussed, and the functions of the ethanol in the synthesis were explored. Besides, the adsorption properties of the as-prepared product toward organic dyes (crystal violet etc.) in water, as well as the sorption isotherms and kinetics, have been investigated carefully. The realizable sorption capacity for crystal violet was found to be 181 mg g À1 which was higher than those of most of the sorbent.