Polyglutamic acid (PE) has been shown to form amyloid fibrils in vitro under pH value of 4.0. However, under the pH of 2.0, a further self-association process resulting in a novel supramolecular structure was observed. These supramolecular assemblies had diameters ranging from 1 to 20 microm and lengths up to several hundred microns, which were significantly larger than those of typical "amyloid fibrils". The existence of amyloid-like structure within these assemblies was confirmed with Fourier transform infrared spectroscopy and Thioflavin T fluorescence assay. The aggregation process of PE was studied by direct observation of electronic microscopy. The supramolecular assemblies appeared to be formed in a hierarchical process in which the preformed amyloid-like subunits self-assembled into higher-order assemblies in a well-organized pattern.