Polyglucuronic acids provide a biocompatible matrix for industries ranging from pharmaceuticals to agriculture. Here we provide a method for selectively producing α-polyglucuronic acid, a simple alternative to the oxidation of cellulose or amylose with 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) or isolation from bacterial cultures. Atomic force micrographs show the pH-dependent formation and persistence of polyglucuronic acid fibrils, while NMR studies demonstrate the selectivity of the glycosidic linkage. By controlling pH, oligoglucuronate chains are created, with both NMR and AFM data showing the preservation of this linkage in basic medium after formation under acid. Clear evidence for the formation of the C–O–C glycosidic bond comes from peaks in the 13C NMR spectra, revealing a linkage through the anomeric carbon atom and also a linkage with a ring carbon atom.